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
  • 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
  • G01S19/22—Multipath-related issues
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
  • G01S19/38—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
  • G01S19/39—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
  • G01S19/42—Determining position
  • G01S19/51—Relative positioning

Definitions

• TITLE Method for detecting masking of one or more satellites, electronic detection device and associated computer program product
• the present invention relates to a method for detecting masking of one or more satellites by an obstacle for a GNSS receiver on board a mobile carrier.
• the present invention also relates to an electronic detection device and a computer program product associated with this method.
• the invention is applicable to the field of tracking the position of mobile object(s) by satellite. More particularly, the invention is applicable for motor and railway land vehicles, maritime vehicles, air vehicles, and for an object carried by a user.
• the positioning of an object can be achieved from a GNSS receiver receiving GNSS signals from satellites.
• GNSS refers to Geolocation and Navigation by a Satellite System.
• An example of such a system is the GPS system (Global Positioning System) or the GALILEO system.
• a satellite is said to be visible to a GNSS receiver, if the GNSS receiver receives GNSS signals from this satellite.
• a satellite is said to be visible and locked if the GNSS receiver produces pseudo-distance measurements between its antenna and that of the satellite and demodulates a navigation message contained in a signal from the satellite.
• the reception, by the receiver, of GNSS signals from 4 separate satellites is generally sufficient to determine the position of the GNSS receiver in space.
• the determination of this position is in particular carried out as a function of the travel time of the GNSS signals originating from each satellite.
• a path traveled by the GNSS signals, transmitted by each satellite and received by the GNSS receiver is substantially linear and direct.
• the signals are said to be direct.
• GNSS signals coming from at least one satellite are likely to bounce off at least one surface of the obstacle or obstacles, before reaching the GNSS receiver.
• Such signals are called indirect, as opposed to direct signals.
• the receiver In the case where the receiver receives, from the same satellite, both direct and indirect signals, the receiver is in a so-called multipath situation.
• NLOS Non Line of Sight
• NLOS situations appear in particular when the mobile carrier carrying the GNSS receiver moves in a cluttered environment.
• a cluttered environment can include any structure, natural or man-made, that may interfere with the path between the GNSS receiver and a satellite.
• the structure masks the satellite, from the point of view of the GNSS receiver. This then leads to a strong attenuation of the amplitude of the direct signals relative to that of the indirect signals.
• Such a situation of NLOS is represented in figure 1 where the direct signals are denoted D and the indirect signals are denoted M.
• the determination of the position of the receiver is impaired. Indeed, the distance between the masked satellite and the receiver is fictitiously lengthened because of the rebound(s) of the signals originating from the masked satellite on one or more surfaces of the structures. In the example of Figure 1, the determined position of the receiver is then the position P'.
• GNSS receiver it is impossible for a GNSS receiver to know a priori whether the GNSS signals received are direct or indirect.
• the object of the invention is therefore to provide a method for detecting masking of one or more satellites.
• the object of the invention is a method for detecting masking of one or more satellites by an obstacle for a GNSS receiver on board a mobile carrier, the method comprising the following steps: continuous reception, at each instant of acquisition and for each of M satellites, of a code pseudo-distance measurement and of a variation of carrier pseudo-distances, M being an integer; calculation of a resolved position of the receiver and a calculated position of each satellite; detection of masking of at least one satellite from the following sub-steps:
• the detection method comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:
• the method comprises, prior to the calculation sub-step, the following steps:
• time of generation of at least one group of N satellites, the satellites of the or each group of N satellites being chosen from among the M satellites, N being an integer less than or equal to M, and
• the detection step includes for each group, the following sub-steps, after the calculation sub-steps:
• the calculation step also includes and for each instant of acquisition, the calculation:
• the generation step includes a selection sub-step, for each satellite, of GNSS signals at each instant of acquisition for which:
• the generation step also includes the following sub-steps:
• the residue calculation sub-step further comprises for each group of satellites:
• the invention also relates to a computer program product comprising software instructions which, when implemented by computer equipment, implement the detection method, as defined above.
• the invention also relates to an electronic detection device comprising technical means suitable for implementing the detection method, as defined above.
• Figure 1 is a schematic view explaining the multi-path problem when geolocating a wearer in a congested environment
• Figure 2 is a schematic view of an electronic detection device, embedded on a carrier, according to the invention
• Figure 3 is a flowchart of a detection method implemented by the detection device of Figure 2;
• Figure 4 is an explanatory diagram of a generation step of the method of Figure 3, illustrated on an example.
• a carrier 5 is mobile in an environment.
• the wearer 5 embeds a GNSS receiver 10 able to receive GNSS signals and an electronic detection device 15 configured to detect masking of one or more satellites and, if necessary, determine a list of satellite(s) masked by an obstacle, during the reception of GNSS signals by the GNSS receiver 10.
• the carrier 5 is for example an aircraft, such as a drone, moving in space in three dimensions, or a land or sea vehicle moving in a plane in two dimensions, or for example a railway vehicle moving in one direction following a railway line.
• aircraft such as a drone, moving in space in three dimensions, or a land or sea vehicle moving in a plane in two dimensions, or for example a railway vehicle moving in one direction following a railway line.
• the GNSS receiver 10 is configured to receive GNSS signals from satellite(s) belonging to the same GNSS system, such as for example the GPS system.
• the GNSS receiver 10 comprises for example a reception antenna 12 known per se and a calculation module 13.
• the antenna 12 is configured to receive GNSS signals from a plurality of satellites and transmit them in the form of electrical signals to the calculation module 13.
• the GNSS signals include, for each satellite S i visible and locked, an identifier of the satellite S i , a transmission time t em,i of the signals by the satellite S i and the ephemeris of the satellite S i .
• Each piece of GNSS signal information is coded on a carrier transmitted by the satellite.
• the calculation module 13 is for example capable of determining the position of the receiver 10 from the GNSS signals using techniques known per se.
• the calculation module 13 is also configured to calculate and transmit to the detection device 15, at each instant of acquisition t h and for each visible and locked satellite S i , the following information: a code pseudo-range measurement PR( i, h ), a carrier pseudo distance variation measurement DR(i, h ) between the acquisition instant t h and a previous instant t h-1 for example according to the equation:
• DR(i, h ) PR car (i, h) - PR car (i, h - 1) where PR car (i, h) is a carrier pseudo-range at the acquisition time t h .
• the calculation module 13 is also configured to transmit to the detection device 15 the ephemeris of each satellite S i and the transmission time of the signals from each satellite S i .
• the acquisition times t h are periodically spaced according to a first predetermined frequency f 1 .
• the detection device 15 comprises an input module 17, a processing module 20 and an output module 25.
• the input module 17, the processing module 20 and the output module 25 are each produced in the form of software stored in one or more storage means (such as a hard disk or a flash disk) and implemented by one or more processors, memory (RAM) and other computer components known per se. These components are then included in the same computer or in different computers/servers. In the latter case, the computers/servers are connected by a local or global network.
• storage means such as a hard disk or a flash disk
• RAM random access memory
• the computers/servers are connected by a local or global network.
• modules 17, 20, and 25 take the form, at least partially, of an independent electronic component, such as for example a programmable logic circuit of the FPGA type (of the English field-programmable gate array) or other.
• an independent electronic component such as for example a programmable logic circuit of the FPGA type (of the English field-programmable gate array) or other.
• the input module 17 is configured to receive, at each instant of acquisition t h , the information calculated by the calculation module 13, namely representative signals.
• the input module 17 is configured to transmit to the processing module 20 the information received.
• the processing module 20 is configured to process the signals, coming from the GNSS receiver 10, in order to detect the presence of a hidden satellite.
• the processing module 20 is configured to determine, if necessary, the list of hidden satellite(s). For this, the processing module 20 is configured to process the GNSS signals as described below in relation to the detection method according to the invention.
• the output module 25 is connected to the processing module 20.
• the output module 25 is configured to transmit to a user or to another electronic device, not shown, information relating to the presence, or absence, of satellite(s). ) hidden(s), and if necessary a list of hidden satellite(s).
• the output module 25 is configured to communicate with a user, this communication takes place, for example, using a screen not shown. In the case where the output module 25 is intended to communicate with another electronic device, the output module 25 is for example intended to communicate with the calculation module 13. The output module 25 is then, for example, configured to send an alert signal to the calculation module 13 in the event of detection of satellites hidden, and if necessary to send to the calculation module 13 the list of hidden satellite(s).
• FIG. 3 presenting a flowchart of this method
• FIG. 4 illustrating a step of the method on an example.
• the carrier 5 moves in a cluttered environment and the GNSS receiver 10 receives, via its antenna 12, GNSS signals from a plurality of satellites.
• the calculation module 13 calculates the information mentioned above and transmits it to the detection device 15.
• the input module 17 receives at each instant of acquisition t h and for each of the M satellites S i the code pseudo-distance measurement PR(i, h) and the variation of carrier pseudoranges DR(i,h).
• the M satellites correspond to the satellites visible and hooked by the GNSS receiver 10.
• the visible satellites are understood here in the sense of satellites whose GNSS signals reach the GNSS receiver 10, without considering whether the GNSS signals, coming from these satellites, travel a path direct or indirect.
• the acquisition step 110 is for example implemented by the input module 17.
• the processing module 20 calculates, for each instant of acquisition t h :
• the processing module 20 has the quantities calculated at each instant of acquisition t h for which the GNSS signals have been received by the receiver 10.
• the calculation step 120 is carried out by the calculation module 13 not included in the detection device 15. The aforementioned calculated elements are then received by the input module 17, from the calculation module 13, and transmitted to the processing module 20.
• the processing module 20 generates, at a generation instant t k , at least one group G j of satellites, and advantageously a plurality of groups G j of satellites.
• the processing module 20 applies for example the following sub-steps, detailed by way of example with reference to FIG. 4.
• the processing module 20 selects for each satellite S i , the data of the GNSS signals at each instant of acquisition t h for which:
• the signal-to-noise ratio C/N0 (i, h ) of the GNSS signals coming from this satellite S i at this acquisition instant t h meets a first criterion; and the elevation angle ⁇ (i, h) of this satellite S i at this instant of acquisition t h meets a second criterion.
• the first criterion is for example that the signal to noise ratio C/N0 (i, h) be greater than 30 dBHz.
• the second criterion is for example that the elevation angle ⁇ (i, h) is greater than 5°.
• the GNSS signals from a satellite S i will only be taken into account in the following sub-steps, at acquisition times t h for which the signal-to-noise ratio C/N0(i, h) of the satellite S i meets the first criterion and the elevation angle ⁇ (i, h) of the satellite meets the second criterion.
• the processing module 20 orders the satellites S i in decreasing order of valid reception duration without discontinuity.
• a valid reception is understood here in the sense of a reception of GNSS signals having been selected during the selection sub-step 131.
• the duration of reception without discontinuity corresponds to a duration since which the input module 17 receives the GNSS signals uninterrupted.
• the processing module 20 classifies the satellites S i by decreasing duration from which their GNSS signals have been selected in an uninterrupted manner.
• the satellite, subsequently named S 1 corresponds to the satellite having the longest valid reception duration without discontinuity.
• the satellite subsequently named S M corresponds to the satellite having the shortest valid reception duration without discontinuity.
• the processing module 20 During a first generation sub-step 133, the processing module 20 generates a first group G 1 of satellites.
• the first group G 1 of satellites comprises N satellites, N being a predetermined integer, advantageously equal to 5 or 6.
• the processing module 20 generates the first group G 1 as comprising the first N satellites S 1 to S N , after their classification during the classification sub-step 132, as represented in FIG. 4 at point a.
• FIG. 4 represents several tables with double entries, of which an abscissa represents the successive acquisition instants t h and an ordinate represents the satellites classified according to their valid reception duration without discontinuity.
• Each box in the table is associated with an acquisition time t h and a satellite S i .
• Each box is either filled in by a statement indicating that a pseudo-range variation of a valid GNSS signal was received at the acquisition time t h for the satellite S i or by a cross in the opposite case.
• the first group G 1 whose data is framed by a bold outline, includes the first five satellites.
• the duration of valid reception without discontinuity of each of the first five satellites corresponds to the difference between the instant of generation t k and the instant t k ⁇ 5 .
• the duration of valid reception without discontinuity of the sixth satellite Se is equal to the difference between the instant of generation t k and the instant t k -2 .
• the valid duration of reception without discontinuity is equal to the difference between the instant of generation t k and the instant t k ⁇ 1 .
• the processing module 20 generates a second group G 2 of satellites, from the first group G 1 of satellites. For this, the processing module 20 generates a group G j comprising the N satellites of the first group G 1 and the satellite, absent from the first group G 1 , having the longest valid reception duration without discontinuity.
• the second group G 2 comprises the first N satellites, and the satellite S N+1 corresponding to the satellite S i absent from the first group G 1 having the longest valid reception duration without discontinuity.
• the second group G 2 of satellites therefore comprises six satellites, namely the first six satellites, after the classification sub-step 132, as outlined in bold at point b.
• the second generation sub-step 134 is reiterated from the second group G 2 of satellites.
• a third group G 3 is generated.
• the third group G 3 comprises each of the satellites of the second group and the remaining satellite having the longest valid reception duration without discontinuity, namely the seventh satellite S 7 .
• the third group G 3 therefore comprises the seven satellites for which data from the GNSS signals have been selected, as represented in bold at point c.
• the second generation sub-step 134 is therefore not repeated a third time.
• the processing module 20 associates a time of birth t n with each group G j of satellites.
• the instant of birth t n corresponds to an instant from which valid GNSS signals, coming from each of the satellites, have been received without discontinuity.
• the instant of birth t n of a respective group G j corresponds to the instant of generation t k minus the shortest valid reception duration without discontinuity among those of each of the satellites of the group G j .
• the instant of birth t n of the first group G 1 is therefore t k-5 because valid signals from each of the satellites have been received, by the input module 17, without discontinuity since this instant t k-5 .
• the instant of birth t n associated with the second group G 2 is instant t k-2 because valid signals have been received without interruption from five of these satellites from instant t k-5 and from valid signals were received without interruption from the sixth satellite S 6 , only from time t k-2 .
• Concerning the third group G 3 for reasons similar to the second group, the instant of birth t n is the instant t k ⁇ 1 .
• the processing module 20 detects the presence of at least one masked satellite, and if necessary, determines the list of masked satellite(s). For this, the processing module 20 analyzes for each group G j , a quantity, called residual, specific to this group G j , by comparison with a first threshold. The residual is obtained from the GNSS signals received from the satellites of this group G j since the instant of birth t n of this group G j .
• the detection step 170 includes the following sub-steps.
• the processing module 20 calculates, for each group G j of satellites, the residue representative of an inconsistency of the signals GNSS received from at least one satellite of this group G j relative to the other satellites of this group G j .
• the processing module 20 calculates, at generation instant t k and at the instant of birth t n , a pseudo-distance calculated respectively PR cal (i, k) and PR cal (i,n), linked to each satellite S i of the group G j , for example according to the formulas:
• the processing module 20 calculates a first estimated position, valid at the generation time t k , by applying a PVT (Position Velocity Time) algorithm known in or, from the code pseudo-distances PR(i, k) and the calculated pseudo-distances PR cal (i, k) of each satellite S i .
• PVT Position Velocity Time
• the processing module 20 calculates, for each satellite S i , a reconstituted pseudo-distance PR′(i,n,k), valid at the time of birth t n , from the variations of carrier pseudo-distance DR( i, h) between the instant of birth t n and the instant of generation t k and from the code pseudo-distance PR(i, k) at the instant of generation t k , for example according to the formula next :
• the processing module 20 also calculates a second estimated position, valid at the instant of birth t n , by application of the PVT algorithm, from the reconstituted pseudo-distances PR′(i,n,k) and the pseudo- calculated distances of each satellite S i .
• the processing module 20 calculates a first pseudo-distance difference vector Z k each component of which corresponds, for each satellite of the group G j , to the difference between the code pseudo-distance PR(i, k) resulting from the GNSS signals received and the calculated pseudo-distance PR cal (i, k) at the instant of generation tk ; and a second pseudorange difference vector
• the first and second pseudo-distance difference vectors are then obtained according to the following formula:
• the processing module 20 also calculates, for the instant of generation t k and for the instant of birth t n , respectively a first H k and a second H n observation matrices, for example according to the following formulas:
• the first Z k respectively the second Z nk , pseudo-distance difference vectors and matrices (H k and H n ) of observation make it possible to define a system of linear equations of which one unknown is a first X k , respectively a second X n,k , position deviation vector of the GNSS receiver at the instant of generation t k , respectively at the instant of birth t n .
• the system of linear equations is then written in the following form:
• Z n,k, H n . Xn ,k ; or :
• the coefficients of the first X k and second X n,k position deviation vectors are the unknowns of the linear system of equations.
• T is the matrix transpose operator; and
• -1 is the matrix inverse operator.
• the processing module 20 calculates the residual as being the difference between approximation errors committed during the calculation of the solution of each of the systems of linear equations by the least squares algorithm.
• the processing module 20 calculates the first and second positions estimated at instants of generation t k and of birth t n from the resolved positions of the receiver at the instants of generation t k and of birth t n at the first and second approximate solutions, according to the equation:
• the processing module 20 then recalculates, for each satellite S i , the calculated pseudo-distance PR cal (i, k) at the instant of generation t k from the first position Position G .(k) and a pseudo- reconstituted calculated distance PR cal '(i, k, n) at the moment of birth t n from the second position according to the formula:
• the processing module 20 calculates the residue according to the formula: which is equivalent to:
• the calculation of the residue is simplified. Indeed, if the position of the GNSS receiver 10 has varied slightly between the instants of birth t n and of calculation t k , then the first H k and second H n observation matrices are substantially similar.
• the calculation module 20 then calculates the approximate solution of the second position deviation vector from the first observation matrix H k . In a similar way, the calculation of the residue is then expressed according to the formula next :
• the processing module 20 detects a masking of at least one satellite of group G j .
• the processing module 20 If, for at least one group G j , the processing module 20 has detected, during the detection sub-step 172, a masking, and the group G j comprises at least six satellites, then the processing module 20 reiterates, during a reiteration sub-step 173, the calculation sub-step 171 for each subgroup of this group G j , then producing a new residue specific to this subgroup.
• Each sub-group is distinct from the other sub-groups and includes all the satellites of the group G j except one.
• a determination sub-step 174 if the new residue of a subgroup is lower than a second threshold while the respective new residues of the other subgroups linked to the same group G j are higher than the second threshold, then the processing module 20 determines a respective masked satellite as being the absent satellite of the sub-group.
• the second threshold is for example equal to the first threshold.
• the processing module 20 detects, during the detection sub-step 172, the masking of at least one satellite of the second group G 2 . If, moreover, the new residue, associated with the subgroup in which the third satellite S 3 is absent, is lower than the second threshold, and the new residues respectively associated with the other subgroups resulting from the second group G 2 are higher than the second threshold, then the processing module 20 determines that the third satellite S 3 is masked.
• the generation 130, association 140 and detection 170 steps are repeated periodically at a second predetermined frequency f 2 .
• the second frequency f 2 is for example equal to the first frequency f 1 .
• the second frequency f 2 is lower than the first frequency f 1 .
• the first frequency f 1 is for example twice the second f 2 . So the steps of generation 130, association 140 and detection 170 are repeated each time the GNSS signals are received by the input module 10 twice.
• the output module 25 communicates to a user or to the calculation module 13, an alert signal if a masked satellite has been detected during the detection step 170.
• output 25 communicates to the user or to the calculation module 13, the list of hidden satellite(s) if it was determined during the detection step 170.
• the detection of hidden satellite(s) is improved because it can be carried out on an on-board system from low computing power, in particular thanks to the formation of group(s) G j .
• the groups G j having a low number of satellites but a long valid reception duration without discontinuity and the groups G j having a short valid reception duration without discontinuity but a large number of satellites allow better masking detection and better determination of the list of masked satellites.
• the selection sub-step 131 makes it possible to ensure that the data coming from the GNSS signals received from the satellites can be used in the detection of masking of satellite(s).

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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)

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• 2020
  • 2020-10-26 FR FR2010946A patent/FR3115608B1/fr active Active
• 2021
  • 2021-10-25 US US18/249,251 patent/US20230393289A1/en active Pending
  • 2021-10-25 EP EP21799258.5A patent/EP4232849A1/de active Pending
  • 2021-10-25 WO PCT/EP2021/079542 patent/WO2022090157A1/fr unknown
  • 2021-10-25 CA CA3196129A patent/CA3196129A1/fr active Pending

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