METHOD FOR GEOLOCALIZING A RECEIVER AND A GEOLOCALIZATION SYSTEM AS WELL AS A CORRESPONDING RECEIVER AND A CORRESPONDING GEOLOCALIZATION SYSTEM COMPLIMENTING WITH SUCH A RECEIVER

Description

[0001] The present invention relates to methods for geolocating a receiver and a geolocation system.

[0002] The present invention also relates to a receiver and a geolocation system comprising such a receiver.

[0003] The field of the invention is that of geolocation in an environment, for example of a person equipped with a receiver in the absence of a global positioning system, for example in the absence of GPS signals.

[0004] This is the case, for example, in certain closed spaces where signals from such a global system cannot reach the receiver.

[0005] This is also the case when signals from a global positioning system are disrupted or jammed, for example intentionally.

[0006] Of course, instead of a person, any other mechanical entity or even an animal whose geolocation is necessary in the environment can be considered.

[0007] In the state of the art, several methods for geolocating a receiver in the absence of a global positioning system already exist. Such methods are described, for example, in Madadi Zahra et al: "Receiver Tracking Using Signs of Opportunity from Asynchronous RF Beacons in GNSS-Denied Environments" and Alexander Ens et al: "Unsynchronized ultrasound system for TDOA localization".

[0008] Among other methods, we know of radiolocation methods based on pre-installed and georeferenced beacons when placed in the environment.

[0009] The receiver's location can be obtained by analyzing the arrival times of different radio signals from these beacons. This technique is known in the prior art as "TDOA" (from the English " Time Difference Of Arrival »).

[0010] According to other methods known from the state of the art, it is possible to geolocate a receiver in such an environment by using distance measurements between the receiver and the various pre-installed beacons also in the environment.

[0011] It is also possible, in the case of movement of several receivers, to implement geolocation of each of them by measuring relative distances between these receivers.

[0012] However, both of the aforementioned types of methods are unsuitable for challenging environments.

[0013] In particular, it is clear that in certain environments, such as wartime environments, the receiver must not be detected by an external system and must therefore not emit radio signals.

[0014] In such a case, geolocation by calculating the distance between the receiver and beacons or between several receivers remains impossible.

[0015] Indeed, there are two strategies: measuring distance by round trip and measuring distance on a single "one way" trip.

[0016] For a round-trip distance measurement, the receiver must be able to transmit signals to beacons or other receivers.

[0017] For a one-way distance measurement, the implementation of the radiolocation technique by measuring the arrival times of signals from different beacons is also difficult to achieve.

[0018] Indeed, to accurately determine the receiver's position, the clocks of the various beacons and the receiver's clock must be synchronized. This is not possible with current onboard clocks, as their accuracy is insufficient to prevent relative drift.

[0019] The aim of the present invention is therefore to enable geolocation of a receiver in constraining environments, in which the reception of external signals is not possible and in which the receiver must move discreetly, i.e. without being detected by a third-party system.

[0020] For this purpose, the invention relates to a method for geolocating a receiver, according to claim 1.

[0021] According to other advantageous aspects of the invention, the geolocation method comprises one or more of the features of claims 2 to 6.

[0022] The present invention also relates to a method for geolocating a geolocation system, according to claim 7.

[0023] The present invention also relates to a receiver comprising technical means configured to implement the geolocation process of this receiver as defined above.

[0024] The present invention also relates to a geolocation system comprising a mobile receiver in an environment and M beacons arranged in the environment, the system being configured to implement the geolocation method of such a system, as defined above.

[0025] These features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which: there figure 1 is a schematic view of a geolocation system according to the invention, the geolocation system comprising a receiver according to the invention and a plurality of beacons; the figure 2 presents on its left side a flowchart of the geolocation process of the geolocation system of the figure 1 and on its right side a flowchart of the geolocation process of the receiver of the figure 1 .

[0026] There figure 1 illustrates in effect a geolocation system 10 according to the invention.

[0027] This geolocation system 10 includes a receiver 12 and M beacons 14-1 to 14-M, the number M being greater than or equal to 3.

[0028] For example, tags 14-1 to 14-M are essentially identical. Therefore, only tag 14-1 will be explained in detail in the following sections.

[0029] As illustrated on the figure 1 The beacon 14-1 includes a radio signal reception / transmission module 21, a processing module 22 and a clock 23. These components of the beacon 14-1 are, for example, contained in a housing equipped with a battery and enabling the autonomous operation of this beacon in a given environment.

[0030] The radio signal receiving / transmitting module 21, for example, has an antenna capable of communicating with the radio signal receiving / transmitting modules of the other beacons 14-1 to 14-M to exchange radio signals.

[0031] The radio signal transmission / reception module 21 is also capable of transmitting radio signals which are intended to be received by any other electronic unit and in particular by the receiver 12 as will be explained later.

[0032] The processing module 22 is capable of determining a location of the beacon 14-1, in particular a relative two-dimensional location, by analyzing radio signals received from the other beacons 14-2 to 14-M as will also be explained later.

[0033] The processing module 22 is also capable of determining radio signals to be emitted by the receiving / transmitting module 21 according to a given periodicity T.

[0034] These signals to be emitted include, in particular, navigation information including the location of beacon 14-1 when it is determined and an identifier of the beacon.

[0035] The identifier of tag 14-1, for example, presents a number or an alphanumeric sequence that allows tag 14-1 to be uniquely identified among the other tags of system 10.

[0036] The clock 23 allows the processing module 22 to count down the value T corresponding to the periodicity of emission of the radio signals including the navigation information.

[0037] The accuracy of clock 23 is known in advance.

[0038] Thus, as is known in the state of the art, the 23 clock can be of good accuracy or of high accuracy.

[0039] In particular, by "good accuracy clock" we mean for example a clock with an accuracy of the order of 10 ppb with, for example, stability of less than 1 ppb.

[0040] By "high precision clock" we mean, for example, a clock with a precision of less than 1 ppb and, for example, a stability of less than 0.1 ppb.

[0041] By "ppb", we mean the unit of measurement known as "parts per billion".

[0042] A person skilled in the art will understand that the above data accuracy and stability values ​​for defining different types of clocks may vary depending on the different applications of system 10.

[0043] In one embodiment, each of the beacons 14-1 to 14-M further includes a barometric module for determining the altitude of the corresponding beacon. The corresponding processing module 22 can then use the measurements provided by this barometric module, along with the radio signals from the other beacons, to determine a three-dimensional location of the beacon.

[0044] According to another embodiment, the receive / transmit modules 21 of at least two beacons 14-1 to 14-M also allow the reception of radio signals from a global positioning system, for example, a global satellite positioning system. In this case, the processing modules 22 of these beacons are adapted to determine an absolute location of the corresponding beacon. Furthermore, in this case, this absolute location can be shared with the other beacons so that each of them becomes capable of determining its own absolute location.

[0045] The receiver 12 includes a receiving module 31, a processing module 32 and a clock 33.

[0046] The receiving module 31, for example, has an antenna capable of receiving radio signals, in particular radio signals from beacons 14-1 to 14-M when these beacons are within the antenna's coverage range.

[0047] The processing module 32 allows the location of the receiver 12 to be determined using radio signals and in particular navigation information carried by the radio signals from the beacons 14-1 to 14-M, as will be explained later.

[0048] Clock 33, for example, is analogous to clock 23 described earlier in relation to beacon 14-1.

[0049] In particular, just like the 23-inch clock, the 33-inch clock can be described as having good accuracy or high accuracy.

[0050] As in the previous case, the same accuracy and stability values ​​can be used to classify clock 33 as having good or high accuracy. Subsequently, clock 33 will be considered to have the same accuracy as the clocks 23 on the beacons.

[0051] Receiver 12 is configured to be worn by a wearer who presents a person or a mechanical device or an animal.

[0052] Receiver 12 can then have a case adapted for this purpose with a corresponding battery.

[0053] According to another embodiment, receiver 12 is integrated into another existing physical entity such as a mobile phone or any other electronic device.

[0054] The geolocation processes of the geolocation system 10 and the receiver 12 will now be explained with reference to the figure 2 presenting the flowcharts of these processes. These processes will subsequently be designated respectively by the numerical references "100" and "200",

[0055] First, it is assumed that the geolocation system 10 is deployed in an environment 40 visible on the figure 1 .

[0056] It is also considered that this environment 40 does not allow the receiver 12 to determine its location using a global positioning system, for example by satellites.

[0057] It is also assumed that beacons 14-1 to 14-M are positioned in environment 40 with movements not known a priori. In other words, these beacons 14-1 to 14-M are not geolocated a priori.

[0058] These tags can for example be placed by a person, for example the person wearing the receiver 12, to allow the geolocation of the wearer in the environment 40 or by any other suitable means.

[0059] Finally, it is considered that the 14-1 to 14-M beacons are arranged consecutively one after the other in a particular direction.

[0060] Thus, for example, in the case of three beacons, the person first places beacon 14-1 then beacon 14-2 and then beacon 14-3 following the clockwise or counterclockwise direction of travel through environment 40. It will therefore be considered that this direction is known by the beacons or is communicated to the beacons by any suitable technical means.

[0061] During an initial step 110 of the geolocation process 100 of the system 10, the beacons 14-1 to 14-M implement one of the known techniques to determine their respective location in the environment 40.

[0062] Thus, for example, these beacons can implement the trilateration technique allowing the location of all beacons by using distance measurements between each pair of beacons.

[0063] The trilateration technique with round-trip ranging measures can be implemented, for example, by constructing a local coordinate system in which: beacon 14-1 is at the origin of the coordinate system; beacon 14-2 is at the point (x2, 0) where x2 corresponds to the distance to beacon 14-1; beacon 14-3 is at the point (x3, y3) where x3 and y3 are calculated taking into account the direction of positioning of the beacons and the distance of this beacon to beacon 14-1 and to beacon 14-2.

[0064] Other beacons can be located in this local coordinate system in a similar way. This system can also be supplemented by a third dimension when these beacons are equipped with a barometric module.

[0065] Furthermore, in the case where at least two beacons can be located absolutely, that is to say in an absolute frame of reference, the other beacons can also determine their location in such an absolute frame of reference.

[0066] The locations of the tags thus determined (relative or absolute) are for example stored at the end of this step 110 in the processing modules 22 of these tags.

[0067] In the following step 120, the processing modules 22 of the beacons 14-1 to 14-M then command the corresponding receive / transmit modules 21 to transmit the corresponding navigation information with the same periodicity T .

[0068] As explained previously, each navigation information includes in particular the determined location of the corresponding beacon as well as its identifier.

[0069] These emissions are carried out asynchronously insofar as the clocks 23 of the beacons 14-1 to 14-M are not synchronized with each other.

[0070] In the following step 130, the receiver 12 locates itself in the environment 40 by implementing the geolocation process 200, the flowchart of which is illustrated in the right-hand part of the figure 2 .

[0071] This process will now be explained in detail.

[0072] During the implementation of this process, it is assumed that the carrier of the receiver 12 moves in the environment 40 according to N successive positions.

[0073] During step 210 of the process, in each of the successive positions N of the carrier 12, the receiving module 31 of the receiver 12 receives the radio signals emitted by all the beacons 14-1 to 14-M.

[0074] Then, this receiving module 31 transmits the received signals to the processing module 32 which then measures the times of reception of each of these signals using its clock 33.

[0075] These measures will subsequently be denoted by the notation TOA ij . In this notation, the index i varies from 1 to N to designate the corresponding position of the holder and the index j varies between 1 and M to designate the beacon from which the corresponding signals are received. In particular, each value of the index j is associated with one of the identifiers of the set of beacons 14-1 to 14-M which is determined by the processing module 32 by extracting this identifier from the navigation information of the corresponding radio signals.

[0076] The measures TOA ij are performed with a measurement noise w which is assumed to be Gaussian with standard deviation σ known and with differential clock instability noise v which is assumed to be negligible.

[0077] Furthermore, during the same step, the processing module 32 also extracts the location of the corresponding beacon from each received navigation information and records it, for example, with the measurement TOA ij corresponding.

[0078] In the following step 220, based on said measurements TOA ij , for each tag j, The processing module 32 determines a first estimate of at least one nuisance parameter relating to the drift of the receiver 12's clock relative to the clock of this beacon j .

[0079] The number of nuisance parameters is chosen based on the accuracy of the clocks 23, 33 of the beacons and the receiver.

[0080] In particular, when high-precision clocks are used, two nuisance parameters α j And δ j for each tag j are chosen.

[0081] For this type of clock, the following drift model is used: q j t = δ j + α j t − t 1 , where t is the current time and t 1 is the initial time.

[0082] For high-precision clocks, the parameter α j is considered negligible and only the parameter δ j is therefore chosen.

[0083] Subsequently, two nuisance parameters will be considered α j And δ j are determined for each beacon j .

[0084] To determine these parameters, processing module 33 applies a maximum likelihood estimator to the following expression: Q X α j δ j T = ∑ i = 1 N ∑ j = 1 M 1 σ 2 δ j + i − 1 T + i − 1 Tα j + d ij c − TOA ij 2 is a is the distance between the beacon j and the receiver in the position i which is also unknown at this stage; c is the propagation speed of radio signals in the environment; and X is the vector of successive positions of the carrier.

[0085] To isolate the parameters α j And δ j the criterion called "minmax" is applied to the expression Q. In other words: argmin Q X = argmin Q X α j δ j = argmin X min α j δ j Q X α j δ j .

[0086] This criterion allows us to estimate the nuisance parameters. α j And δ j as follows: δ j = − 2 2 N − 1 v j + 6 w j N N + 1 ; α j = − 2 v j + Nδ j N N − 1 T − 1 ; with : v j = ∑ i = 1 N d ij c − TOA ij ; w j = ∑ i = 1 N i d ij c − TOA ij .

[0087] During step 230, implemented for example simultaneously with step 220, the processing module 33 determines, for each beacon and in each receiver position, a second estimate corresponding to the distance estimate. is a between this beacon and receiver 12 in this position.

[0088] These second estimates are determined using the estimator Q the aforementioned measures TOA ij and nuisance parameters, using for example the least squares criterion.

[0089] Then, in the next step 240, the processing module 32 determines the location of the receiver 12 in at least one of the N positions from the locations of the beacons 14-1, ..., 14-M and the distances is a corresponding.

[0090] In particular, such a location P and = ( x , this ) of the receiver in the position i is determined using the following expression: d ij = Cx j − x i 2 + Cy j − y i 2 Or

[0091] C j = ( Cx j , Cy j ) is the relative or absolute two-dimensional location of the beacon j .

[0092] It is therefore clear that the location P and the receiver is a relative location in the local coordinate system when the positions C j are relative and an absolute location in the absolute coordinate system when the positions C j are absolute.

[0093] The present invention therefore offers a number of advantages.

[0094] First, the invention makes it possible to geolocate the receiver in a constraining environment in which the reception of geolocation signals from an external geolocation system is not possible or is complicated.

[0095] To achieve this, the invention proposes to place in such an environment beacons which locate themselves relative to each other by emitting signals containing their position periodically.

[0096] The receiver can then receive these signals to deduce its location in the environment without having to emit signals in response, even with clocks operating asynchronously.

Claims

1. Geolocation method (200) for a receiver (12) moving in an environment (40) comprising M beacons, the number M being greater than or equal to 3, each beacon (14-1, ..., 14-M) being identifiable by an identifier and capable of periodically transmitting radio signals carrying navigation information comprising the identifier of that beacon (14-1, ..., 14-M) and its location in the environment (40), each of the receiver (12) and the M beacons (14-1, ..., 14-M) having a clock (23, 33); the method (200) comprising the following steps: - in each of the N successive positions of the receiver (12) in the environment (40), collection (210) of M measurements, each measurement corresponding to the time of arrival of the radio signals carrying the navigation information from one of the beacons (14-1, ..., 14-M); - from the said measurements, for each beacon, determination (220) of a first estimate corresponding to the estimate of at least one nuisance parameter relating to the deviation of the clock of the receiver (12) with respect to the clock of this beacon (14-1, ..., 14-M); - on the basis of the said measurements and the said first estimates, for each beacon (14-1, ..., 14-M) (12), determination (230) of a second estimate corresponding to the distance between that beacon (14-1, ..., 14-M) and the receiver (12) in that position; - determination (240) of the location of the receiver (12) in at least one of the N positions from the locations of the beacons (14-1, ..., 14-M) and the distances between these beacons (14-1, ..., 14-M) and the receiver (12) in that position; where the first and second estimates are determined by a maximum likelihood estimator; and in which the first estimates are functions of the second estimates.

2. Geolocation method (200) for a receiver (12) according to claim 1, in which the beacons (14-1, ..., 14-M) are able to transmit the said radio signals asynchronously with the same transmission period.

3. Geolocation method (200) for a receiver (12) according to claim 2, in which the estimator is applied to the following expression: Σ i = 1 N Σ j = 1 M 1 1 σ 2 δ j + i − 1 T + i − 1 Tα j + d ij c − TOA ij 2 where TOAij is a measurement of the time of arrival of the radio signals carrying the navigation information from beacon j in the receiver's position i; dij is the distance between beacon j and the receiver in position i; c is the propagation speed of the radio signals in the environment; T is the period of transmission of the radio signals by the beacons; σ is a standard deviation of the noise of said measurements; αj and δj are nuisance parameters relating to the deviation of the receiver's clock with respect to the clock of beacon j.

4. Geolocation method (200) for a receiver (12) according to any one of the preceding claims, in which the number of nuisance parameters of each first estimate is chosen as a function of the accuracy of the corresponding clocks (23, 33).

5. Geolocation method (200) for a receiver (12) according to claim 4, in which: - a nuisance parameter is chosen when the accuracy of the corresponding clocks (23, 33) is less than 1 ppb; - two nuisance parameters are chosen when the accuracy of the corresponding clocks (23, 33) is in the region of 10 ppb.

6. Geolocation method (200) for a receiver (12) according to any one of the preceding claims, in which the said location of the receiver (12) is determined with respect to a local reference frame defined by the beacons (14-1, ..., 14-M) or with respect to an absolute reference frame when the locations of at least two of the M beacons (14-1, ..., 14-M) are determined within this absolute reference frame.

7. Geolocation method (100) for a geolocation system (10) comprising a mobile receiver (12) in an environment (40) and M beacons (14-1, ..., 14-M) arranged in the environment (40), the number M being greater than or equal to 3, each beacon (14-1, ..., 14-M) being identifiable by an identifier; the method (100) comprising the following steps: - determination (110) of the respective locations of the beacons (14-1, ..., 14-M) in the environment (40); - each beacon (14-1, ..., 14-M) periodically transmits radio signals (120) carrying navigation information, including the identifier of that beacon (14-1, ..., 14-M) and its location in the environment; - movement of the receiver (12) and determination (130) of its location in the environment by the geolocation method (200) according to any one of claims 1 to 6.

8. Receiver (12) comprising technical means configured to implement the geolocation method (200) according to any one of claims 1 to 6.

9. Geolocation system (10) comprising a mobile receiver (12) in an environment (40) and M beacons (14-1, ..., 14-M) arranged in the environment; the system (10) being configured to implement the geolocation method (100) according to claim 7.