Method for locating a receiver within a positioning system

Abstract

A method for locating at least one receiver in a positioning system. The system includes: at least two generators, each generator emitting, on a single carrier, at least two signals that each have a different code, and a receiver configured to detect the signals emitted by the generators. In the method: the receiver measures, for each generator, the phase difference between both signals emitted by the generator, and at least one geometric size, representing the position of the receiver in relation to the generators, is calculated on the basis of the measurements of the phase difference in order to locate the receiver in the positioning system.

Claims

1. A method for locating at least one receiver within a positioning system, the system comprising: at least two generators, each generator emitting, on one and the same carrier, at least two signals each having a different code, and a receiver configured to detect the signals emitted by the generators, in which method: the receiver measures, for each of the generators, the phase difference between the two signals emitted by the generator, and depending on these phase difference measurements, at least one geometric quantity is calculated that is representative of the position of the receiver with respect to the generators in order to locate the receiver within the positioning system.

2. The method as claimed in claim 1, wherein the two signals emitted by each generator are emitted from two emission areas of the generator that are separated from one another by a predefined distance.

3. The method as claimed in claim 2, wherein the geometric quantity representative of the position of the receiver with respect to a generator is the angle of arrival of the signals emitted by the generator at the receiver, dependent on the predefined distance between the two emission areas of the generator and on the phase difference measurements, and defined by: ${}_j=\mathrm{Arc}\cos \left(\frac{{}^j}{d_{12}^j}\right).$

4. The method as claimed in claim 1, wherein the geometric quantity representative of the position of the receiver with respect to a generator is the distance separating them, dependent on the distances between the position of each emission area of the generator and the position of the receiver, which positions are defined by:
d.sub.2d.sub.1={square root over ((x.sub.a2x.sub.r).sup.2+(y.sub.a2y.sub.r).sup.2)}{square root over ((x.sub.a1x.sub.r).sup.2+(y.sub.a1y.sub.r).sup.2)}=.

5. The method as claimed in claim 1, wherein the two signals emitted by each generator originate from at least two antennae belonging to the generator and separated from one another by a predefined distance.

6. The method as claimed in claim 5, wherein the predefined distance by which the two antennae of one and the same generator are separated from one another is equal to the carrier wavelength of the signals emitted by the antennae.

7. The method as claimed in claim 1, wherein the signals emitted by one and the same generator are synchronized with one another.

8. The method as claimed in claim 1, wherein each generator emits on a different frequency.

9. The method as claimed in claim 1, wherein the frequency of the signals emitted by the generators is equal to 1.575 GHz, the signals in particular being of Galileo GNSS type.

10. The method as claimed in claim 1, being implemented indoors.

11. A positioning system, including: at least two generators, each generator emitting, on one and the same carrier, at least two signals each having a different code, and a receiver detecting the signals emitted by the generators, the system being configured such that: the receiver measures, for each of the generators, the phase difference between the two signals emitted by the generator, and depending on these phase difference measurements, at east one geometric quantity representative of the position of the receiver with respect to the generators is calculated in order to locate the receiver within the positioning system.

12. A receiver intended to be used within a positioning system comprising at least two generators, each generator emitting, on one and the same carrier, at least two signals each having a different code, the receiver detecting the signals emitted by the generators, the receiver being configured: to measure, for each of the generators, the phase difference between the two signals emitted by the generator, and such that, depending on these phase difference measurements, at least one geometric quantity representative of the position of the receiver with respect to the generators is calculated in order to locate the receiver within the positioning system.

13. The receiver as claimed in claim 12, having a phase-locked loop that is configured to measure the phase of the signals emitted by the generators.

14. A generator intended to be used within a positioning system, said system comprising at least one other generator and a receiver configured to detect the signals emitted by said generator and the other generator, said generator being configured to emit, on one and the same carrier, at least two signals each having a different code, the receiver being configured to measure the phase difference between said two signals emitted by the generator.

Description

(1) The invention will be able to be better understood upon reading the following description of non-limiting exemplary implementations thereof, and upon examining the appended drawing, in which:

(2) FIG. 1 schematically shows a positioning system in which a method according to the invention is able to be implemented,

(3) FIG. 2 shows the geometry implemented in a positioning system according to the invention,

(4) FIGS. 3 to 5 are curves showing the performance of the method according to the invention,

(5) FIG. 6 schematically shows a positioning system, according to the prior art, using pseudolites,

(6) FIG. 7 illustrates steps for implementing a variant of the method according to the invention,

(7) FIG. 8 schematically shows a positioning system in which a variant of the method according to the invention is able to be implemented, and

(8) FIG. 9 illustrates a resultant receiver path obtained by implementing a variant of the method according to the invention.

(9) FIG. 1 shows an example of a positioning system 1 in which the invention is able to be implemented.

(10) The system comprises a receiver 2 and three generators PL1, PL2, PL3 forming a local constellation. The system 1 is able to be implemented indoors, for example inside a building, or outdoors in a highly urban area, between very high walls for example. Each generator PL1, PL2, PL3 emits, in the example described, on one and the same carrier, two signals each having a different code. The emitters may be the generators described previously. These two signals are emitted from two emission areas PL1.sub.1, PL1.sub.2 of the generator PL1 that are separated from one another by a predefined distance d.sub.12. In the example described, and preferably, the two signals emitted by each generator PL1, PL2, PL3 originate from two antennae belonging to the generator and that are separated from one another by a predefined distance equal to the wavelength of the carrier of the signals emitted by the antennae.

(11) The signals emitted by one and the same generator are preferably synchronized with one another. Each generator PL1, PL2, PL3 preferably emits on a different frequency. The signals emitted by the generators PL1, PL2, PL3 are GNSS signals with a frequency equal to 1.575 GHz, for example.

(12) The receiver 2 is configured to detect the signals emitted by the generators. Said signals are for example received by the antenna of the receiver 2 and then amplified and converted to an intermediate frequency FI that is lower than their initial frequency.

(13) In the example under consideration, these signals are sampled and then digitized before being processed by the reception channels of the receiver 2, which is multi-channel. These reception channels may implement tracking loops. The receiver 2 advantageously has a phase-locked loop that is configured to measure the carrier phase .sub.k of the signals emitted by the generators.

(14) The receiver 2 is advantageously configured to measure, for each of the generators PL1, PL2, PL3, the phase difference .sup.j between the two signals emitted by the generator PLj.

(15) As defined previously, depending on these phase difference .sup.j measurements, the receiver 2 is advantageously configured to calculate at least one geometric quantity representative of the position of the receiver with respect to the generators PL1, PL2, PL3, in order to obtain its position (x.sub.r, y.sub.r) within the system 1.

(16) In the example of FIG. 2, and as defined previously, the geometric quantity representative of the position (x.sub.r, y.sub.r) of the receiver 2 with respect to a generator PLj is the angle of arrival CI, of the signals emitted by the generator PLj at the receiver, dependent on the predefined distance d.sub.12.sup.j between the two emission areas of the generator and on the phase difference .sup.j measurements:

(17) ${}_j=\mathrm{Arc}\cos \left(\frac{{}^j}{d_{12}^j}\right).$

(18) In one variant, the geometric quantity representative of the position (x.sub.r, y.sub.r) of the receiver 2 with respect to a generator PLj is the distance separating them, dependent on the distances (d.sub.1, d.sub.2) between the position (x.sub.a1, y.sub.a1, x.sub.a2, y.sub.a2) of each emission area PLj.sub.1, PLj.sub.2 of the generator PLj and the position (x.sub.r, y.sub.r) of the receiver 2: d.sub.2d.sub.1={square root over ((x.sub.a2x.sub.r).sup.2+(y.sub.a2y.sub.r).sup.2)}{square root over ((x.sub.a1x.sub.r).sup.2+(y.sub.a1y.sub.r).sup.2)}=.

(19) FIGS. 3 to 5 show results obtained by implementing the invention in a hail measuring 20 m by 20 m, in which the two generators PL1 and PL2 are positioned at the positions (0, 0) and (20, 0), thus being positioned on the same side of the hall.

(20) The method according to the invention is implemented, as defined previously, in order to locate a receiver 2 located at the coordinates (5; 15) of the hall. Around 660 phase difference measurements are performed in order to evaluate the performance of the method according to the invention,

(21) FIG. 3 shows the distribution of the position errors per measurement, corresponding to the distance between the calculated position of the receiver 2 and its actual position. According to FIG. 3, the precision of the positioning seems to be centered on around thirty centimeters.

(22) FIG. 4 shows the distribution of the position errors as a function of the signal phase measurement errors.

(23) FIG. 5 shows the positions of the receiver 2 that are calculated according to the invention in the plane Oxy, the sought point being shown by a square at the coordinates (5, 15) and the various calculated points being represented by light rhombi. Moving averages over 10 points have been carried out, shown by triangles, making it possible to confirm that the precision of the positioning is of the order of around thirty centimeters. The dark rhombus represents the overall average of the point obtained over the 650 measurements, which point happens to be 7.5 cm away from the actual position of the receiver 2.

(24) FIG. 8 shows an example of a system 1 in which the method according to a variant of the invention, steps of which are illustrated in FIG. 7, is able to be implemented.

(25) The system 1 comprises a receiver 2 that is mobile within the system 1 and a plurality of emitters PL1, PL3, PL4 forming a local constellation. As shown in FIG. 6, the system 1 is able to be implemented indoors, for example inside a building, or outdoors in a highly urban area, between very high walls for example.

(26) Each emitter PL1, PL2, PL3, PL4 preferably emits a signal comprising a code-modulated carrier. The emitters may be the generators described above. In this case, a single antenna per generator is advantageously considered.

(27) As explained previously and as shown in FIG. 7, during a step 11, a predefined estimated initial position {circumflex over (X)} is chosen for the receiver 2. During its movement within the positioning system 1, on the basis of this estimated initial position, during a step 12, the receiver 2 performs successive measurements of the carrier phase .sub.k of the signal emitted by each emitter PL1, PL2, PL3, PL4 for various subsequent positions of the receiver (x.sub.j, y.sub.j, z.sub.j).

(28) During a step 13, the variations of the carrier phase of the signals between each subsequent position of the receiver 2, for which position the phase .sub.k has been measured, and the estimated initial position of the receiver are calculated for each emitter PL1, PL2, PL3, PL4. The matrix d defined previously is created during a step 13b is.

(29) In order to calculate the variation in distance X between the receiver 2 and the emitters and to determine the actual initial position of the receiver 2 within the positioning system 1, the matrix H defined previously is created during a step 14 and is inverted during a step 15. The variation in distance X is calculated during a step 16.

(30) The variation in distance X thus calculated and the predefined estimated initial position {circumflex over (x)} of the receiver 2 are added together during a step 17 in order to form a new initial position {circumflex over (x)}.

(31) During a step 18, the variation in distance X is compared with a second predefined threshold .sub.2. If X is greater than this second predefined threshold, the predefined estimated initial position {circumflex over (x)} of the receiver 2 is modified, the phase and phase variation measurements being reiterated on the basis of this new estimated initial position.

(32) If X is smaller than this second predefined threshold .sub.2, it is compared with a first predefined threshold .sub.1, the method according to the invention advantageously being reiterated, starting from step 14, for as long as the variation in distance X between the receiver and the emitters is greater than this first predefined threshold.

(33) When the variation in distance X between the receiver 2 and the emitters is smaller than the first predefined threshold .sub.1, it is checked, during a step 19, whether the initial position of the receiver determined in this way belongs to the region covered by the positioning system 1 and delimited by the positions of the emitters.

(34) If the determined initial position of the receiver belongs to the region covered by the positioning system 1, the estimated initial position {circumflex over (X)} of the receiver 2 is retained as the actual position during a step 20; if not, the method is reiterated.

(35) The first predefined threshold is between 10.sup.5 m and 10.sup.1 m, for example equal to 10.sup.2 m. The second predefined threshold is between 10.sup.2 m and 10.sup.5 m, for example equal to 10.sup.3 m.

(36) FIG. 9 shows the results obtained by implementing the invention in an urban canyon in the shape of a U measuring 20 m by 30 m, formed by tall buildings. In this example, four emitters are deployed on the top floor of the buildings, at a height of around 18 m.

(37) A receiver 2 is moving in this environment. The receiver 2 has an estimated initial position P0, and then performs an outward-return trip between the positions P0 and P3, passing via the subsequent positions P1 and P2, then goes from position P0 to position P4. The method for locating the receiver 2 according to the invention is implemented, and the positions obtained are compared with the actual path, as is visible in FIG. 9. The reconstructed path obtained is very close to the actual path, which is known beforehand for the purposes of the experiment, the gap remaining below 50 cm, as displayed in the table below showing the error and the average error for each position.

(38) TABLE-US-00001 PR(m) Average Position X(m) Y(m) Error(m) error EHDOP P0 4.04 14.82 0.44 0.05 26.7 P1 4.39 17.56 0.43 0.05 P2 5.61 20.78 0.40 0.06 P3 8.8 24.15 0.13 0.28 P4 4.09 3.37 1.08 0.23 P4c 3.72 4.00 0.73 0.23 4.2

(39) Positions P3 and P4 give the greatest errors because they are more difficult to estimate due to the configuration of the path, corresponding to a multipath and cycle slips building up sources of error. The method according to the invention has thus been used to correct position P4 by using an additional measurement at an intermediate position between P3 and P4, leading to the result P4c in the table above, giving a smaller error.

(40) The last column of the table shows the results obtained for the extended horizontal dilution of precision, a value that specifies the influence of the geometry of the environment on the precision of the positioning system and that is adjusted to the method according to the invention, thus representing the influence of the measurement error on the initial position of the receiver. By considering that the errors with regard to each phase measurement are Gaussian errors centered at zero, and that these errors are distributed identically for each emitter and are independent of one another, the extended horizontal dilution of precision is able to be calculated from the formula: cov(.sub.X)=(H.sup.tH).sup.1.sub.UERE.sup.2, where cov(.sub.X) is the error covariance matrix with regard to the estimated position of the receiver, and .sub.UERE.sup.2 is the error variance with regard to the measurement, or user equivalent range error. By denoting the elements cov(.sub.X) with .sub.ij and the elements (H.sup.tH).sup.1 with Dij, we obtain:

(41) 0$\mathrm{EHDOP}=\sqrt{D_{11}+D_{22}}=\frac{\sqrt{{}_{11}+{}_{22}}}{{}_{\mathrm{UERE}}}.$

(42) An extended horizontal dilution of precision value of between 10 and 40 is considered to be acceptable, and the results obtained for positions P0 to P4 are therefore correct. However, the extended horizontal dilution of precision value obtained for position P4c defined above is excellent. This shows that it is beneficial and necessary to use the method according to the invention over the course of the movement of the receiver within the system in order to reduce errors that build up along the path.

(43) As explained previously, the number of emitters n.sub.pl of the system 1 is dependent on the dimension m of the positioning and on the number of measurements k.sub.pt carried out for different positions of the receiver 2:

(44) $m.Math.\left(1+\frac{1}{k_{\mathrm{pt}}}\right)n_{\mathrm{pl}}.$
For example, for m=3, corresponding to 3D positioning, the minimum number of emitters n.sub.pl is equal to 5 if three different positions are used to perform three measurements k.sub.pt: 3(1+)=4. If only one measurement k.sub.pt is used, in order to ascertain the position of the receiver quickly, it is necessary to have: 3(1+1)=6 emitters.

(45) The invention is not limited to the examples that have just been described.

(46) Signals other than GPS and GNSS signals may be used, for example 4G, GSM or radio signals.

(47) The methods according to the invention may be combined with other geopositioning methods, such as methods using a mobile reader, beacons and a geopositioning and guidance application able to be executed on said reader.

(48) The invention may be implemented in locations where team sports are played, in particular indoors, for example by fixing or incorporating a system into football or handball courts in order to calculate the position of the players in real time, or on construction sites, for example for the installation of false ceilings, by using one or more rulers formed by a network of around ten antennae, or in large shopping malls.

(49) The invention may be used outdoors, making it possible to dispense with base stations.

(50) The expression having a must be understood as a synonym for the expression comprising at least one, except when the opposite is stipulated.