Collaborative navigation and radio transmission for a swarm of vehicles

Abstract

The present invention relates to a network (100) comprising a plurality of entities (1), each entity (1) forming a node of the network (100), wherein each entity (1) comprises: - a location device (2) configured to generate a location signal (200); - a clock (3) configured to generate a time datum (205) indicative of the generation time of the location signal (200); and - a data processing device (4) configured to determine, by means of the location signal (200) and the time datum (205), the propagation time of the location signal (200) between two entities (1) of the network (100) and to deduce therefrom the distance between the two entities (1).

Description

[0001] DESCRIPTION

[0002] TITLE: Collaborative navigation and radio transmission for swarms of vehicles

[0003] TECHNICAL FIELD

[0004] This presentation concerns the general field of geolocation of an entity in a network of entities which may include in particular one or more vehicles, for example autonomous vehicles, a fixed station, etc. so as to precisely establish the position of the entities.

[0005] This disclosure relates more particularly, but not exclusively, to a method enabling precise geolocation of an autonomous aircraft within a network of autonomous aircraft as well as time synchronization of the autonomous aircraft within this network.

[0006] STATE OF THE ART

[0007] Current vehicle guidance systems use navigation systems that determine the vehicle's position at regular intervals to compare it with the trajectory to be followed. This position is generally determined using a receiver of an absolute satellite positioning system, such as GNSS (Global Navigation Satellite System) systems like GPS or Galileo, which offer accuracy limited to a few meters and can be jammed.

[0008] Additionally, when vehicles move in groups, for example in the case of aerial drones flying in swarms, the vehicles in the group communicate with each other via a radio link or other means of communication in order to exchange their position and trajectory. Each entity in the group then knows the absolute position of the other members and deduces the distance separating them. This information is used to maintain a minimum safety distance in order to avoid collisions and control the trajectory (if applicable) of the vehicles. Other methods can be used to measure the distance between two vehicles, such as measuring the intensity of the received signal (Received Signal Strength Indicator or RSSi).

[0009] However, when the distances between vehicles are small, for example when the drones in the swarm are in close formation and the space between them is less than one meter, the accuracy of GNSS and RSSI systems is insufficient and the risk of collision is therefore high.

[0010] STATEMENT OF THE INVENTION

[0011] An aim of the invention is to remedy the aforementioned drawbacks, by proposing a network comprising a plurality of entities, each entity forming a node of the network, in which each entity comprises:

[0012] - a location device configured to generate a location signal;

[0013] - a clock configured to generate time data indicative of a time of generation of the location signal; and

[0014] - a data processing device configured to determine, using the location signal and the time data, a propagation time of the location signal between two entities of the network and to deduce a distance between the two entities.

[0015] The network according to the invention is advantageously supplemented by the following characteristics, taken independently or in one of their technically possible combinations: each entity further comprises a transmitter-receiver device configured to transmit and receive the location signal and the time data, each device for locating an entity further comprises a satellite positioning system and at least one of an inertial unit and an optical sensor, the location signal then comprising a position of the entity.

[0016] The invention also relates to an entity forming a node of a network, the entity comprising:

[0017] - a location device configured to generate a location signal;

[0018] - a clock configured to generate time data indicative of a time of generation of the location signal; and

[0019] - a data processing device configured to determine, using the location signal and the time data, a propagation time of the location signal of another entity in the network and to deduce a distance between the two entities.

[0020] The entity according to the invention is advantageously completed by the following characteristics, taken independently or in one of their technically possible combinations: a transmitter-receiver device configured to transmit and receive the location signal and the time data, a satellite positioning system and at least one of an inertial unit and an optical sensor, the location signal then comprising a position of the entity.

[0021] The invention also relates to a method for locating an entity of a network according to the invention, comprising the following steps: generating a location signal of an entity of the network; generating a time data item indicative of a time of generation of the location signal; receiving, by at least one other entity, the location signal and the time data item; and from the location signal and the time data item, determining a propagation time of the signal between the entity of the network and the at least one other entity of the network and deducing therefrom a distance between the entity of the network and the at least one other entity of the network.

[0022] The location method according to the invention is advantageously supplemented by one or more of the following steps: a step of time synchronization of the entities with a reference clock, the reference clock being able to correspond to a clock of one of the entities of the network; a step of absolute location of all or part of the other entities of a network to obtain an absolute position of the entities; a step of determination, by trilateration from the absolute position of four entities of the network, of an absolute position of a fifth entity of the network.

[0023] Advantageously, the steps of receiving the location signal and determining a propagation time are implemented by several other entities in the network.

[0024] The step of determining a propagation time can also include the use of a Kalman filter.

[0025] The invention also relates to a method for guiding a vehicle comprising the following steps:

[0026] - locate the absolute position of an entity of a network, the entity including the vehicle; and

[0027] - vehicle guidance.

[0028] The invention also relates to a method for synchronizing a network transmission security system, comprising the following steps:

[0029] - generate time data indicative of a signal generation time;

[0030] - receive, by at least one other entity, the temporal data; and

[0031] - from the time data, synchronize the transmission security system of the entity and at least one other entity.

[0032] DESCRIPTION OF THE FIGURES Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0033] Figure 1 is a schematic overview illustrating a network according to one embodiment of the invention;

[0034] Figure 2 is a schematic view of the systems of a network entity according to one embodiment of the invention;

[0035] Figure 3 is a schematic view of the systems of another network entity in accordance with an embodiment of the invention;

[0036] Figure 4 is a schematic view of the power as a function of time of a waveform of a signal transmitted by a network entity according to an embodiment of the invention;

[0037] Figure 5 is a schematic overview illustrating a set of dissimilar entities belonging to the network, according to one embodiment of the invention;

[0038] Figure 6 is a schematic overview illustrating a set of entities belonging to the network, according to one embodiment of the invention;

[0039] Figure 7 is a schematic overview illustrating the guidance of a network entity according to one embodiment of the invention;

[0040] Figure 8 is a flowchart illustrating steps of an exemplary method of locating a network entity according to an embodiment of the invention;

[0041] Figure 9 is a flowchart illustrating steps of an exemplary method of guiding a network entity according to an embodiment of the invention;

[0042] Figure 10 is a flowchart illustrating steps of an exemplary method of synchronizing the transmission security system of a network entity according to an embodiment of the invention.

[0043] Throughout the figures, similar elements have identical references.

[0044] DETAILED DESCRIPTION OF THE INVENTION

[0045] In the following, the present description will relate more particularly to a network 100 comprising a plurality of entities 1, for example autonomous aircraft. This is not limiting, the description applying to any other type of entity 1, such as land vehicles or any fixed or mobile equipment, autonomous or not.

[0046] The network 100 thus comprises a plurality of entities 1, each entity 1 forming a node of the network 100, that is to say that each entity 1 constitutes the infrastructure or the material support of a point of redistribution or endpoint of the information communicated on the network 100.

[0047] The network 100 is preferably an ad-hoc network, for example of the flying ad hoc network type (“Flying Ad hoc Networks FANETs” in English terminology) or of the vehicle ad hoc network type (“VANETs” in English terminology), that is to say that the network 100 is decentralized and that the entities 1 propagate the information transmitted between them according to a routing established dynamically and autonomously. This allows each entity 1 to communicate with all the other entities 1 of the network 100 within communication range.

[0048] Each entity 1 comprises a location device 2 configured to generate a location signal 200, a clock 3 configured to generate a time data item 205 indicative of a time of generation of the location signal 200 and a data processing device 4 configured to determine, using the location signal 200 and the time data item 205, a propagation time of the location signal 200 between two entities 1 belonging to the network 100 and to deduce therefrom a distance between the two entities 1.

[0049] More precisely, each entity 1 of the network 100 iteratively generates a location signal 200 associated with a time data item 205. The time data item 205 can be a timestamp indicating precisely the instant of generation of the location signal 200.

[0050] Preferably, the entities 1 comprise a transmitter-receiver device 5. Each entity 1 equipped with a transmitter-receiver device 5 can broadcast its location signal 200 to any member of the network 100 within its range, without discrimination (in "broadcast" according to English terminology). Furthermore, each entity 1 can receive the location signal 200 from the entities 1 within range via its transmitter-receiver device 5. The transmitter-receiver device 5 may, for example, comprise a radiofrequency communication device. In the remainder of this description, an entity 1 receiving a location signal 200 from another entity 1 is called a receiver entity 1 a, while the other entity 1 is called a transmitter entity 1 b, 1 c, 1 d, 1 e.

[0051] Thus, in order to determine the distance between the receiving entity 1a and a transmitting entity 1b, the data processing device 4 of the receiving entity 1a receives from the transmitting entity 1b a time data item 205 associated with a location signal 200. The time data item 205 is compared to its time of reception, in order to obtain a time difference which constitutes a precise estimation of the flight time (propagation time) of the location signal 200 (according to the method called “time of arrival”). The time difference obtained makes it possible to deduce the relative distance between the entities 1a and 1b by multiplying the time difference by the speed of the location signal 200. This relative distance is also called the relative position of the transmitting entity 1b with respect to the receiving entity 1a.The accuracy of measuring this distance depends directly on the accuracy of the 3 clocks, which are synchronized for optimal precision.

[0052] To ensure the accuracy of the measurement of the distance between two entities 1 by the data processing device 4, it is preferable that the clocks 3 are all synchronized with respect to a reference clock 31, which is for example an atomic or microatomic clock. The synchronization of the clocks 3 of the network 100 can be carried out by following a precise time protocol (“Precision Time Protocol PTP” in English terminology) of the IEEE 1588v2 standard. The reference clock 31 preferably has an accuracy of the order of 10 nanoseconds, which allows a distance measurement accurate to approximately 30 centimeters. The reference clock 31 may in the present example be carried by an entity 1 which then also comprises a precise time server 32, which ensures within the network 100 the distribution of the time and frequency of the reference clock 31 in broadcast, that is to say the synchronization and the tuning of the clocks 3 of the other entities 1.Of course, the precise time server 32 can be integrated into any type of entity 1 belonging to the network 100, for example a ground station, fixed or mobile. When a member of the network 100 is out of direct communication range of the precise time server, the time and frequency of the reference clock 31 can be relayed to it by other entities 1 of the network 100 within range of the transmitter-receiver device 5 of the entity 1 comprising the precise time server 32.

[0053] On the other hand, the location device 2 of each entity 1 may also comprise a satellite positioning system 21, for example a GNSS. The satellite positioning system 21 is optionally hybridized with an inertial unit 22 or an optical sensor 23, the optical sensor 23 in this case performing a resetting on a fixed reference point, or landmark. Thus, the entity 1 can determine its position from this satellite positioning system 21 and communicate it within the location signal 200 to the entities 1 of the network 100 within range of the transmitter-receiver device 5. The position is associated with the time data 205, which is then indicative of the time of determination of the position.

[0054] In this case, the data processing device 4 of a receiving entity 1 a receiving from a transmitting entity 1 b a location signal 200 comprising such an absolute position implements a fusion (or hybridization) method, to obtain a precise absolute position from the fusion of the relative and absolute positions of the transmitting entity 1 b.

[0055] The location signal 200 can therefore comprise in its waveform, as illustrated in FIG. 4, an increasing ramp 201 of signal power increase, an overshoot 202, a preamble 203, a mode 204, the time data 205, the position and / or the absolute position 206, a data sequence 207 and a decreasing ramp 208 indicating the end of the location signal 200 to the location device 2. The waveform incorporates the time data 205 at the level of its physical layer and at the level of these MAC layers the protocol of the IEEE 1588v2 standard.

[0056] The network 100 makes it possible to precisely locate any entity 1 thanks to the implementation, for example by the data processing device 4 of a receiving entity 1a, of a location method S which can comprise the following steps.

[0057] During a step S1, the location device 2 generates a location signal 200 of the entity 1a of the network 100, the location signal 200 being able to comprise the position of the entity 1a, for example in the form of coordinates provided by its location device 2.

[0058] During a step S2, a time data item 205 indicative of a time of generation of the location signal 200 is generated using the clock 3 of the entity 1 a. Where appropriate, the time data item 205 is then indicative of the time of determination of the position by the location device 2.

[0059] During a step S3, the transmitter-receiver device 5 of the receiver entity 1a receives the location signal 200 and the time data 205 transmitted by the transmitter-receiver device 5 of another entity 1b. The location signal 200 may symmetrically comprise the position of the other entity 1b, a position determined by a location device 2.

[0060] During a step S4, the data processing device 4 uses the time data 205 to determine a propagation time of the signal between the entity 1 a and the entity 1 b in order to deduce therefrom the relative distance between the entity 1 a and the other entity 1 b. In other words, the distance between the entity 1 a and the entity 1 b is calculated as described previously, using the time of flight of the location signal 200 as well as the propagation speed of the location signal 200. The optional use by the data processing device 4 of the receiving entity 1 a of a Kalman filter makes it possible to further improve the accuracy of the measurement of the relative distance. Furthermore, the relative distance between the entities 1 a, 1 b is also calculated from their position determined by the location device 2, broadcast and time-stamped in broadcast. The propagation time can then be deduced from this relative distance.If necessary, a Kalman filter can be used.

[0061] Advantageously, the relative distance between the entities 1 a and 1 b can also be obtained by an entity 1 a from the position broadcast within the location signal 200 of the other entity 1 b, by calculating the distance between the position of the unit 1 a and the position of the unit 1 b. This second relative distance can be used to calculate a second propagation time of the location signal 200 between the entities 1 a and 1 b, by dividing the second relative distance by the propagation speed of the signal. This second propagation time can be merged or hybridized with the propagation time deduced from the time data 205, in order to obtain a more precise propagation time. The use of this more precise propagation time in the calculation of the distance between the entities 1 a and 1 b makes it possible to further improve the accuracy of the calculation of step S4.

[0062] Optionally, the clocks 3 of the entities can be time synchronized during a step S0, which is preferably a precise time protocol of the IEEE 1588v2 standard. This synchronization makes it possible to measure the distances between the entities 1 a and 1 b with better precision. If necessary, the clocks 3 can be synchronized during the step S0 with respect to a reference clock 31 to further improve the location accuracy.

[0063] During a step S5, the position of the other entity 1 b broadcast within the location signal 200 is merged with the relative distance of this entity 1 b and the position of the entity 1 a to obtain a more precise position, called absolute position 206 of the other entity 1 b. More precisely, the entity 1 a uses its coordinates from its location device 2, the coordinates of the other entity 1 b contained in the location signal 200 and the relative distance of the other entity 1 b calculated in step S4 to determine the absolute position 206 of the other entity 1 b, which is more precise than the position obtained only by a location device 2 or by the use of the relative distance. Advantageously, the absolute position 206 can therefore be used to recalibrate an inertial unit 22.

[0064] Of course, the location method S can be implemented simultaneously by all or part of the entities 1 of the network 100, so that each entity 1 knows the relative distance of all or part of the other entities 1 and their absolute position 206.

[0065] In particular, the location method S can be implemented to determine the position of a receiving entity 1 a not comprising a functional location device 2, from the absolute position 206 of four transmitting entities 1 b, 1 c, 1 d and 1 e respectively equipped with location device 2. For this, during a step S6, the data processing device 4 of the receiving entity 1 a uses the distances between the four transmitting entities 1 b, 1 c, 1 d and 1 e of the network 100 to determine an absolute position 206 of the receiving entity 1 a by trilateration.

[0066] The synchronization of the clocks 3 with a reference clock 31 allowing increased precision in the measurement of the relative distance, the network 100 makes it possible to compensate for the inaccuracy of the location provided by the satellite positioning system 21 thanks to step S5 and therefore allows each entity 1 to accurately determine the location of the other entities 1 members of the network 100. This is particularly advantageous in the case where the entities 1 are autonomous drones flying in close formation or swarm. In the case where the entities 1 are vehicles, the entities 1 further comprise a guidance unit 7. The network 100 then allows the guidance of a receiving entity 1a from another transmitting entity 1b by implementing a guidance method E from the determination of the absolute position 206 of the receiving entity 1a thanks to the location method S previously described.

[0067] The transmitting entity 1 b then generates guidance instructions for the receiving entity 1 a as a function of the absolute position 206 thus determined. If the receiving entity 1 a is an autonomous vehicle, the guidance instructions may be received by a piloting unit 71 of the receiving entity 1 a which then generates appropriate commands to modify the trajectory of the vehicle. Otherwise, when the receiving entity 1 a is a piloted vehicle, the guidance instructions may for example be displayed on an interface visible to the pilot.

[0068] The iterative implementation of the location method S allows the transmitting entity 1 b, from the successive absolute positions of the receiving entity 1 a, to know a trajectory, a speed and an acceleration of the receiving entity 1 a. The guidance instructions can then be generated in order to maintain a predetermined safety distance 9 between the entity 1 a and the other entities 1 b, 1 c, 1 d, 1 e of the network 100.

[0069] This guidance method E can also be used, for example, in the case of a landing method. In this case, the transmitting entities 1 b, 1 c, 1 d and 1 e can be fixed stations and a landing point 10 can be designated as a point equidistant from these four stations. The guidance instructions can then include immobilization instructions when the absolute position 206 of the receiving entity 1 a is that of the equidistant point 10.

[0070] Alternatively, if none of the entities 1 a, 1 b, and 1 c includes a satellite positioning system 21 or if the latter cannot establish their position, for example in the event of interference, the network 100 still makes it possible to implement a guidance method E using only the relative position of each entity. From the successive relative positions of each entity 1 a, 1 b, and 1 c with respect to the others, trajectories, speeds and relative accelerations of the entities 1 a, 1 b, and 1 c can be established. Guidance instructions can then be generated in order to maintain the predetermined safety distance 9 between the entity 1 a and the other entities 1 b and 1 c of the network 100 by comparing the respective relative distances with the predetermined safety distance 9.

[0071] On the other hand, the synchronicity of the clocks 3 of the entities 1 of the network 100 makes it possible to implement a method for synchronizing a security system 51 of the transmissions transmitted and received by the entities 1 within the network 100. For this, a time data 205 indicative of an instant of generation of a synchronization signal is generated. The signal transmitted by a first entity 1 is received by another entity 1 via their respective transmitter-receiver device 5.

[0072] At least one other entity 1 receives the time data 205. A security system 51 for the transmissions of the entity 1 and of the at least one other entity 1 is synchronized based on this time data 205. The security system 51 is for example a TRANSEC type device (“transmission security” in English terminology) controlling frequency hops in the frequencies used by the transmitter-receiver devices 5 of the entities 1. The time synchronization then allows more precise frequency hops, which reduces delays and limits possible losses of communication between the entities 1 and increases the security of their exchanges.

[0073] The network 100 allows, thanks to the temporal data 205 exchanged by the entities 1, a precise localization of the entities 1 and the implementation of the methods described, which offer numerous additional advantages, among which a precision of less than one meter in the determination of the relative positions between the entities 1, the sharing of the positions and trajectories of each of the entities 1, the coordination of movement in close formation when the entities 1 are vehicles thanks to the respect of a predetermined safety distance, the securing of transmissions. The network 100 therefore allows the localization, navigation and temporal synchronization of the entities 1 ("Position Navigation Timing" in English terminology) with a precision much higher than existing systems.

[0074] These advantages are particularly evident when a first entity 1 is a weapon aircraft carrying several second entities 1 which are munitions. The weapon aircraft, comprising a reference clock 31 and a satellite positioning system 21, serves as a reference node for the distribution of precise time and as a reference point for navigation to other entities of the network 100, which cannot include these elements for reasons of carrying capacity or cost.

[0075] Subsequently, the munitions separate from the weapon aircraft. The network 100 then makes it possible to measure the relative location between the different entities 1 and to have the absolute positions of each of the entities.

[0076] In the event of a temporary communication breakdown, the network 100 makes it possible, via the radio connections established by the transmitter-receiver devices 5 of the entities 1, to re-establish precise time synchronization, to determine the relative location of the entities 1 step by step and to broadcast the absolute positions of each of the entities 1 within range to the other entities via the network 100.

Claims

CLAIMS 1. Network (100) comprising a plurality of entities (1), each entity (1) forming a node of the network (100), in which each entity (1) comprises: - a location device (2) configured to generate a location signal (200); - a clock (3) configured to generate a time data item (205) indicative of a time of generation of the location signal (200); and - a data processing device (4) configured to determine, using the location signal (200) and the time data (205), a propagation time of the location signal (200) between two entities (1) of the network (100) and to deduce therefrom a distance between the two entities (1).

2. Network (100) according to claim 1, wherein each entity (1) further comprises a transceiver device (5) configured to transmit and receive the location signal (200) and the time data (205).

3. Network (100) according to one of claims 1 or 2, in which each location device (2) of an entity (1) further comprises a satellite positioning system (21) and at least one of an inertial unit (22) and an optical sensor (23), the location signal (200) then comprising a position of the entity (1).

4. Entity (1) forming a node of a network (100), the entity (1) comprising: - a location device (2) configured to generate a location signal (200); - a clock (3) configured to generate a time data item (205) indicative of a time of generation of the location signal (200); and - a data processing device (4) configured to determine, using the location signal (200) and the time data (205), a propagation time of the location signal (200) of another entity (1) of the network (100) and to deduce therefrom a distance between the two entities (1).

5. Entity (1) according to claim 4, further comprising a transmitter-receiver device (5) configured to transmit and receive the location signal (200) and the time data (205).

6. Entity (1) according to one of claims 4 and 5, in which the location device (2) further comprises a satellite positioning system (21) and at least one of an inertial unit (22) and an optical sensor (23), the location signal (200) then comprising a position of the entity (1).

7. Method for locating S an entity (1 b) of a network (100) according to one of claims 1 to 3, comprising the following steps: 51: generating a location signal (200) of an entity (1a) of the network (100); 52: generate a time data item (205) indicative of a time of generation of the location signal (200); 53 receive, by at least one other entity (1 b), the location signal (200) and the time data (205); and 54: from the location signal (200) and the time data (205), determine a propagation time of the signal between the entity (1a) of the network (100) and the at least one other entity (1b) of the network (100) and deduce therefrom a distance between the entity (1a) of the network (100) and the at least one other entity (1b) of the network (100).

8. Location method S according to claim 7, comprising a step S0 of time synchronization of the entities (1) with a reference clock (31), the reference clock (31) being able to correspond to a clock (3) of one of the entities (1) of the network (100).

9. Method for locating S an entity (1 a) by another entity (1 b) according to one of claims 7 and 8, in which steps S3 and S4 are implemented by several other entities (1 b, 1 c, 1 d, 1 e) of the network (100).

10. Location method S according to one of claims 7 to 9, in which step S4 comprises the use of a Kalman filter.

11. Location method S according to one of claims 9 to 10, further comprising a step S5 of absolute location of all or part of the other entities (1 b) of a network (100) to obtain an absolute position (206) of the entities (1).

12. Location method S according to claim 11, further comprising a step S6 of determining, by trilateration from the absolute position (206) of four entities (1 b, 1 c, 1 d, 1 e) of the network (100), an absolute position (206) of a fifth entity (1 a) of the network (100).

13. Method for guiding E a vehicle (1) comprising the following steps: - locate the absolute position (206) of an entity (1) of a network (100) according to the claim 12, the entity (1) comprising the vehicle (1); and - vehicle guidance (1).

14. Method for synchronizing P a security system (51) of transmissions of a network (100) according to one of claims 1 to 3, comprising the following steps: - generate time data (205) indicative of a signal generation time; - receive, by at least one other entity (1), the temporal data (205); and - from the time data (205), synchronize the security system (51) of the transmissions of the entity (1) and of the at least one other entity (1).

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