Technical Field

The invention relates to a relative positioning method for the calculation of the distance, azimuth and elevation angles between platforms/autonomous vehicles and the estimation of the relative position by using Ultra Wide Band (UWB) signal receivers in a multiple antenna array structure.

In the method of the invention, position estimation is performed between swarm members during Ultra Wide Band based communication between autonomous swarm members. The relative position information of each autonomous swarm member with respect to the other swarm members is available, in order to maintain the formation of autonomous swarms.

Prior Art

The technique basically uses the Global Navigation Satellite System (GNSS) for positioning the members of the swarm. Such solutions are also strengthened by supporting them with a camera.

Today, the use of autonomous vehicles to fulfil various tasks by forming a swarm has increased. Autonomous swarm members in this swarm need to be positioned in order to maintain the swarm structure in adequate way. Positioning applications are carried out by GNSS method with an accuracy of (6m, 1 sigma). GNSS requires open space with access and has a weakness against signal jamming. Positioning applications can be performed with the Global Navigation Satellite System - Real Time Kinematics (GNSS-RTK) method with an accuracy of (1cm, 1 sigma), but this application also has a weakness against signal jamming. In addition, the GNSS- RTK method requires a pre-installation, such as an external antenna that takes long- term measurements at a fixed location, which is costly in terms of time, space and money.

Received Signal Strength (RSS) method can be used via Bluetooth/Wi-Fi for positioning autonomous vehicles, but this method has low performance in terms of accuracy (1-10 metres, 1 sigma).

United States document US10534068B2, which is in the known state of the art, discloses a vehicle positioning system according to various aspects. The document mentions at least 3 UWB anchors (fixed UWB measurement unit with known position). With UWB units, only distance measurements are made. Using the distances measured with these anchors of known position, position estimation is performed by multilateration method. In the present application, the position of the reference unit does not need to be known. In addition, in the current application, the antenna array is used for direction estimation as well as distance measurement and positioning is performed by trigonometric equations. In the document, a coordinate system is established with 3 UWB units and other UWB units are positioned with reference to this coordinate system. In the current application, there are no fixed UWB anchors and each UWB unit is positioned relative to another UWB unit.

United States Patent No. US201625259032A1, which is in the known state of the art, discloses a positioning apparatus that uses time-stamped signals transmitted by transceivers that are part of a distributed localisation system to calculate its position relative to transceivers. The document includes UWB anchors at a fixed point. In the current application, there are no fixed UWB anchors and each UWB unit is positioned relative to another UWB unit.

Chinese Patent CN113516708A, which is in the known state of the art, mentions a precise spatial positioning method for a transmission line inspection aircraft, which belongs to the field of sensing equipment positioning and machine vision applications. The document uses camera image and fixed anchor positioning method. In the current application, there are no fixed UWB anchors and each UWB unit is positioned relative to another UWB unit.

When the existing studies in the technique are examined, it is necessary to perform a relative positioning method in which the distance, azimuth and elevation angles between autonomous swarm members are calculated by using Ultra Wide Band (UWB) technology in a multiple antenna array structure (dual, triple, quad antenna structure), in order to qualify the swarm to create, maintain and change formation.

Objects of the Invention

The object of the present invention is to develop a relative positioning method using Ultra Wide Band (UWB) technology with multiple antenna arrays (dual, triple, quadruple antenna structure) to calculate the distance, azimuth and elevation angles between autonomous swarm members, thus enabling the swarm to establish, maintain and change a formation.

Another object of the invention is to develop a relative positioning method, which provides a three-dimensional, comprehensive and precise positioning solution by simultaneously taking distance and angle measurements over Ultra Wide Band (UWB), while at the same time transmitting data such as orientation, barometer and altitude information if required.

Another object of the invention is to enable autonomous swarm members to be positioned relative to each other and/or to a mobile reference member within the swarm, while sharing critical non-positioning information (battery status, health status, route information, operational orders, etc.) between the swarm members.

Another object of the present invention is to enable the estimation of the position of any one of the members of an autonomous swarm in a spherical coordinate system and the estimation of the position of all the members of the swarm, which are positioned relative to each other, in a spherical coordinate system. Another object of the present invention is the realisation of a relative positioning method that can be performed in a fixed position in addition to moving devices and can be used for safe autonomous landing.

Detailed Description of the Invention

The relative positioning method for achieving the objects of the present invention is shown in the accompanying figures.

These figures;

Figure 1: Schematic view of the hardware units of the autonomous swarm members used in the method of the invention.

Figure 2: Schematic view of the UWB inter-unit distance measurement calculations used in the inventive method.

Figure 3: Schematic view of the layout of the dual antenna array used in the inventive method and the incoming UWB signal angle calculations.

Figure 4: Schematic view of the layout of the triple antenna array used in the inventive method and the incoming UWB signal angle calculations.

Figure 5: Schematic view of the layout of the quad antenna array used in the inventive method and the incoming UWB signal angle calculations.

Figure 6: Schematic view of the dual antenna array layouts and coverage areas in 3D space used in the inventive method.

Figure 7: Schematic view of the triple antenna array layouts and coverage areas in 3D space used in the inventive method.

Figure 8: Schematic view of the quad antenna array layouts and coverage areas in 3D space used in the inventive method. The systems in the figure are numbered one by one and the corresponding numbers are given below.

1. UWB Unit

2. Autonomous Processing Computer

3. Inertial Measurement Unit (6 degrees of freedom gyroscope and accelerometer and 3 degrees of freedom magnetometer)

4. Barometer

5. Autonomous Driving/Flight Controller

6. Unmanned Aerial Vehicle (UAV)

7. Unmanned Ground Vehicle

8. UWB Module

9. UWB Unit Microprocessor

The invention relates to a relative positioning method using ultra-wide band (UWB) technology in autonomous swarms, comprises the steps providing intra-swarm communication via ultra-wide band (UWB) unit (1), through the receiving antenna tree and transmitting antenna, evaluating the simultaneously received signal with the phase difference of arrival (PDoA) and the time difference of arrival (TDoA) methods and making bearing estimation,

- the mutual communication of ultra-wide band (UWB) units (1) is ensured and the distance between the units is found by multiplying with the time of flight (ToF) method the flight time of the ultra- wide band (UWB) signal by the speed of the signal in the air, fusion of distance and bearing information obtained from the ultra-wide band (UWB) unit (1), orientation data obtained from inertial measurement units (3) and, when three-dimensional positioning is required, height data obtained from the barometer (4) with the autonomous processing computer (2) to perform relative positioning, obtaining the relative position information of each swarm member with respect to other swarm members from the received ultra-wide band (UWB) messages, feedback of the device's autonomous driving controller (5) via the autonomous processing computer (2) based on the difference between the calculated relative position information and the relative position information to be found according to maintaining the order , movement of the autonomous vehicle (unmanned aerial vehicle (6) and unmanned ground vehicle (7)) using the information supplied to the autonomous driving controller (5), correction of the position information of the autonomous vehicle (unmanned aerial vehicle (6) and unmanned ground vehicle (7)).

In the method of the invention, the UWB unit (1) provides communication within the swarm through the receiving antenna array and the transmitting antenna, simultaneously measuring the angle of arrival of the received signal and the distance between the signal source and the signal source with the time information in the content. The UWB unit (1) contains the UWB module (8) and the UWB unit microprocessor (9), which calls the functions of the UWB module (8) and transfers the data.

The autonomous swarm members' autonomous processing computer (2) is a computer with high processing power. It calculates its own relative position in the swarm with the data received from the UWB unit (1), inertial measurement units (3) and barometer (4) (when three-dimensional positioning is required). It processes the position information of the other swarm members transmitted in UWB messages and transfers the necessary driving information to the autonomous driving controller (5) according to the order it needs to maintain. In addition, when there is pre-planned route information or when the swarm member needs to be controlled by remote control, the autonomous processing computer (2) provides the movement of the autonomous vehicle (unmanned aerial vehicle (6) and unmanned ground vehicle (7)) through the autonomous driving controller (5).

In scenarios where the swarm member, who is accepted as the leader within the swarm, has a predetermined route or is managed by remote control, it will be possible to protect any predetermined formation by performing relative positioning within the swarm. The difference between the calculated relative position information and the relative position information that should be found according to the formation to be protected is fed back to the driving controller (5) of the device via the autonomous processing computer (2). (The necessary driving information is transferred to the autonomous driving controller (5) by the autonomous processing computer (2)).

The relative position of the device obtained from distance, angle, orientation and height data is calculated as x, y, z in 3D space with respect to the reference/leader vehicle. The x, y, z position is calculated according to the formation (driving order) information previously determined or given to the device at that moment. The autonomous driving controller (5) performs acceleration/deceleration/turning movement according to the current orientation information of the unmanned aerial vehicle (6) and unmanned land vehicle (7) and the required position.

The autonomous vehicle (unmanned aerial vehicle (6) and unmanned ground vehicle (7)) also includes a barometer (4) and inertial measurement units (3). The inertial measurement units (3) and the barometer (4) are used as auxiliary units during relative positioning within the swarm (when three-dimensional positioning is required).

The autonomous driving controller (5) controls the movement units of the autonomous swarm member with the data coming from the autonomous processing computer (2).

Positioning with Ultra Wide Band (UWB) signals, distance calculation is performed using the ToF method. PDoA and TDoA methods are also used to calculate the signal arrival angle. With this calculated information, the position information of other autonomous swarm members can be calculated. The method of the invention makes it possible to position the swarm devices by using different number of receiver antennas and transferring data between the devices, thus ensuring the organisation of the swarm. The distance calculation formulas (Formulas I and II) between autonomous vehicles used in UWB units (1) are shown below. The accuracy of the measurements taken as a result of this distance calculation is (20cm, 1 sigma) for a range of 50 metres. The simplest version of the distance measurement protocol is shown in Figure 2. The variables represent the time intervals between sent and received UWB messages required for the distance measurement procedure, as shown in Figure 2. (Time of Flight (ToF) _DS is the time the UWB signal spends in the air and is calculated using the time intervals between messages. (I) The calculated ToF is multiplied by the speed of light (c) to obtain the distance between two UWB units. (II)

(TIR: arrival time of initial message, TRR: arrival time of reply message, TFR: arrival time of final message, TIT: transmission time of initial message, TRT: transmission time of reply message, TFT: transmission time of final message, c: speed of light in the medium)

Two basic measurement methods, PDoA and TDoA, are used to determine the angle of arrival of UWB signals. Both methods require an antenna array. PDoA is the measurement of the phase difference between the antennas of the signal arriving at the antenna array. TDoA is the measurement of the time difference between the antennas of the signal arriving at the antenna array. High sensitivity is achieved by using these two methods variably between certain approach angles. Depending on the antenna array to be used, the coverage areas that can be measured in 3D space are given in Figures 6-8.

The angle and distance information between the UWB units (1) obtained as a result of the placement of the antenna array of the UWB unit (1) in the autonomous vehicle (unmanned aerial vehicle (6) and unmanned ground vehicle (7)) as shown in Figure 4 is not sufficient for the three-dimensional positioning of all autonomous swarm members in autonomous vehicle swarms. In order to calculate the distance between autonomous swarm members, it is sufficient for a receiving antenna to use the method in Figure 2. The azimuth and elevation angles between autonomous swarm members vary depending on the number of receiving antennas. In the method of the invention, these positionings are calculated by separate methods depending on the number of receiving antennas.

In the method of the invention, when the UWB module (8) has a dual antenna structure, the phase difference (PDoA) and time of arrival (To A) of the signals reaching the UWB unit (1) are recorded and the angle of the incoming signal is estimated according to the time difference (TDoA) and phase difference (PDoA) recorded by these two antennas. In the case of two antennas, the azimuth angle solution space contains only the front or rear semicircle. Information about the elevation angle cannot be obtained from the antenna array. This ambiguity can be resolved by sharing the orientation information via UWB units (1), having two swarm members orientated in the same direction in the horizontal plane, and then looking at the change in the distance between them according to the information received from the acceleration and deceleration of a swarm member in this direction. (If one reference swarm member is considered stationary and the other autonomous swarm member increases its speed in the same horizontal direction and the distance between them increases accordingly, the moving autonomous swarm member is considered to be in the lead.)

The calculation of the elevation angle does not have a solution space for the two- antenna method. This information required for three-dimensional positioning is obtained by adding a barometer (4) connected to the autonomous processing computer (2) on the autonomous swarm member and transferring the height information received from here to the other autonomous swarm member via UWB message.

In the method of the invention, the relative positioning of the UWB module (8) in the dual antenna structure is realised with the help of the following formulae.

(<p: azimuth angle, 0: elevation angle, T ₁₂ : arrival time difference, c: speed of light due to the medium, d: distance between antennas on the UWB module)

Due to the dual antenna structure, angles in the range [0, 7t] can be detected for the azimuth angle (<p) (III). Due to the dual antenna structure, no angle detection is possible for the elevation angle (0) (IV). The difference between the arrival time at the nearest antenna (ti) and the arrival time at the second antenna (t2) according to the direction of arrival of the signal is the antenna arrival time difference (T ₁₂ : TDoA) (V). The product of the arrival time difference (T ₁₂ ) and the ambient speed of light (c) is equal to the inter-antenna distance (d) multiplied by the cosine of the azimuth angle. (VI) The azimuth angle is obtained by the trigonometric solution of the arrival time difference (T ₁₂ ), the ambient speed of light (c) and the inter-antenna distance (d) (VII).

In the method of the invention, in the case where the UWB module (8) is in the triple antenna structure, the azimuth and elevation angles of the UWB signal arriving at the antenna array are found. The approach angles of the incoming UWB signals are calculated by PDoA and TDoA methods. In the case of three antennas, all angles of arrival in the upper or lower hemisphere can be detected. In order to provide three-dimensional positioning, data transfer between autonomous swarm members is also provided, and the hemisphere in which the swarm member is located relative to a reference swarm member can be calculated based on the solution of height sharing with the barometer (4) or the upward movement of the other swarm member in the vertical direction while the orientation of both swarm members is the same. (For example, if the reference swarm member is stationary while the other autonomous swarm member moves up and the distance between them decreases, the other autonomous swarm member can be found to be in the lower hemisphere compared to the reference).

In the method of the invention, when the UWB module (8) has a quad antenna structure, one antenna must be positioned at a point separate from the plane formed by the other three antennas in order to provide a solution covering the entire sphere. The angle of arrival of the incoming UWB signals is calculated by PDoA and TDoA methods. With this method, a full sphere positioning solution can be obtained.

In the method of the invention, the relative positioning of the UWB module (8) in the case of a triple antenna structure is realised with the help of the following formulae.

Due to the triple antenna structure, angles in the range of [0, 2K] can be detected for the azimuth angle (<p) (VIII). Due to the triple antenna structure, the elevation angle (0) can be determined in the range [0, K/2] (IX). The approach angle of the signal can be calculated by processing the time or phase difference data from the three antennas using the least mean square (LMS) method (X), (XI).

In the method of the invention, the relative positioning of the UWB module (8) in the quad antenna structure is realised with the help of the following formulae.

Due to the quad antenna structure, it is possible to determine the angle in the range of [0, 2π] for the azimuth angle (φ ) (XII). Due to the quad antenna structure, the elevation angle (θ) can be determined in the range [-K/2, K/2] (XIII). The approach angle of the signal can be calculated by processing the time or phase difference data from the four antennas using the least mean square method (XIV), (XV). The inventive method comprises a network management solution for the calculation of different positioning of the swarms according to the scenarios. With this network management, the following features are provided to the swarm:

- Positioning calculations and transfer of necessary data,

The relative position of each autonomous swarm member relative to the other swarm members in the swarm is shared by all swarm members,

- Members can be added/removed from the swarm,

The need for close-range movement of the swarm according to the scenario, The need for faster movement of the swarm according to the scenario.

Network management offers different solutions with TDMA and ALOHA-like methods to provide flexible swarm member structure and to share the location information of each swarm member with other members. With these solutions, a healthy UWB messaging can be maintained while providing swarm communication.

In the method of the invention, the autonomous processing computer (2) performs sensor fusion with the orientation and altitude data in 9 degrees of freedom received from the UWB unit (1) and the sensors in the autonomous swarm member, and then performs the relative positioning algorithm within the swarm. After the swarm relative positions are calculated, the swarm order preservation algorithm is applied. Thus, the autonomous swarm members maintain the swarm order by using each relative position.

The inventive method can be used in autonomous swarm navigation applications and indoor outdoor swarm positioning applications. In addition, in the method, Ultra Wide Band (UWB) signals are used to measure the precise distance (20cm, 1 sigma) and angle (azimuth, elevation: 5°, 1 sigma) between the devices, thus obtaining precise positioning information between autonomous swarm members. This information can be used in autonomous vehicle swarm flight control applications, autonomous vehicle swarm driving control applications, autonomous vehicle automatic landing applications. It can be used in military/civilian air/land/sea operations in situations where autonomous swarm members forming a swarm need to move in a certain way and communicate for small-sized (payload) data sharing at the same time. For this situation, a route to be followed can be assigned to a swarm member to be selected from the swarm, or this swarm member can be manually managed remotely. The route to be assigned to this selected swarm member can also be made to be followed via GNSS, but since the inventive method will perform positioning with UWB signals, it will maintain the driving order in the absence of GNSS access. At the same time, if the assigned route is in a closed environment, the formation of the swarm will be protected by precise positioning and small-sized (payload) data will be shared between them.