Method and system for determining a relative position between platforms

Abstract

The present disclosure relates to a method for determining a relative position between a first platform and a second platform comprising establishing (310) a communication link between the first platform (101) and the second platform (102); transmitting (311) a request for a positional signal from the first platform (101) to the second platform (102); transmitting (320) a positional signal from the second platform (102) utilizing a transducer, wherein the positional signal has a radiation pattern comprising at least one lobe; determining (330), using a computer (220) comprised in the first platform (101), an orientation change over time for a transducer of the first platform (101); simultaneously measuring (350) the transmitted positional signal from the second platform (102) with the transducer of the first platform (101), and performing the determined orientation change of the transducer; and calculating (370), by one or more computers, the relative position (140) for the first platform (101) and the second platform (102) based on the measured positional signal and measured signal strength values, and the performed orientation change.

Description

[0001] Method and system for determining a relative position between platforms

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to determination of relative positions, signal strength measurement, transducer, antenna radiation patterns, direction finding, radiolocation, radiopositioning, time difference of arrival, received signal strength indicators, signal strength matching, and time-of-flight distance measurements.

[0004] BACKGROUND ART

[0005] Ranging utilizing electromagnetic waves or material waves typically involves determining the distance between two points by measuring the time it takes for a wave to travel from a transmitter to a receiver. In order to determine a relative difference in position further information relating to relative bearing is typically needed.

[0006] Radio direction finding, also known as direction finding, is a technique used to determine the direction from which a received radio signal was transmitted. This method involves using a directional antenna to scan the radio spectrum and identify the direction of the signal source. By taking measurements from multiple locations, or using a single moving platform, the position of the transmitter may be triangulated. Radio direction finding is utilized in various fields, including navigation for maritime and aviation purposes, search and rescue operations, and military intelligence. Corresponding possibilities and challenges exist when utilizing sonar to find relative positions between platforms.

[0007] There is a need to provide improved solutions to determine the relative position between a transmitter and a receiver.

[0008] SUMMARY OF THE INVENTION

[0009] One object of the invention is to provide a relative position between platforms.

[0010] This has in accordance with the present disclosure been achieved by means of method for determining a relative position between a first platform and a second platform. The method comprises

[0011] - establishing a communication link between the first platform and the second platform;

[0012] - transmitting a request for a positional signal from the first platform to the second platform;

[0013] - transmitting a positional signal from the second platform utilizing a transducer, wherein the positional signal has a radiation pattern comprising at least one lobe;

[0014] - determining, using a computer comprised in the first platform, an orientation change over time for a transducer of the first platform;

[0015] - simultaneously measuring the transmitted positional signal from the second platform with the transducer of the first platform, and performing the determined orientation change of the transducer by controlling a motion control system of the first platform and / or by controlling a transducer orientation system; and

[0016] - calculating, by one or more computers, the relative position for the first platform and the second platform based on the signal-strength values of the measured positional signal, and the performed orientation change.

[0017] This has the advantage of allowing relative position between a first platform and a second platform based on the relative orientation changes of the antenna arrangements of the platforms.

[0018] In some embodiments, establishing the communication link comprises determining an estimated distance between the platforms based on time-of-flight, and wherein calculating the relative position is further based on said determined estimated distance.

[0019] In some embodiments, the estimated distance between the platforms is determined using timestamped transmissions and a precise clocks comprised in each platform, and utilizing time- of-flight to estimate the distance.

[0020] This has the advantage of allowing an improved accuracy in the determined relative position between a first platform and a second platform.

[0021] In some embodiments, calculating the relative position comprises combining

[0022] - information indicative of signal-strength values of the measured positional signal over time, and

[0023] - information indicative of the performed orientation change over time, to form a matching curve relating to signal strength as a function of orientation for the performed orientation change, and wherein said matching curve is compared to corresponding predetermined radiation pattern metrics relating to the positional signal to calculate the relative position.

[0024] This has the advantage of allowing the measured positional signal to be compared to a digital model of the radiation pattern in order to improve the determined relative position between a first platform and a second platform.

[0025] In some embodiments, the matching curve comparison is further based on the estimated distance between the platforms. This has the advantage of allowing further improved determination of matching with the digital model of the radiation pattern.

[0026] In some embodiments, the method comprises performing at least one additional iteration of simultaneously measuring the transmitted positional signal from the second platform and performing a different orientation change of the transducer, wherein calculating the relative position between the first platform and the second platform is further based on information indicative of said radiation pattern and determined signal strength values for said at least one additional iteration.

[0027] This has the advantage of allowing the information from two or more different orientation changes to further improve determination of matching with the digital model of the radiation pattern. This further has the advantage of reducing the uncertainty in the determined relative position between a first platform and a second platform in at least some directions.

[0028] In some embodiments, the step of transmitting the positional signal comprises at least one timestamp, platform ID, and / or lobe ID, and wherein

[0029] - measuring comprises determining said at least one timestamp, platform ID, and / or lobe ID, and

[0030] - calculating the relative position is based on said determined at least one timestamp, platform ID, and / or lobe ID.

[0031] This has the advantage of allowing the first platform to more readily determine the source of the received positional signal and / or to more readily determine the radiation pattern or lobe being used.

[0032] In some embodiments, the first platform is a mobile platform and the orientation change is performed at least in part by an orientation change of said first platform, and wherein, during measuring of the positional signal, information indicative of the orientation change performed is determined utilizing an IMU and / or an INS comprised in the first platform.

[0033] This has the advantage of allowing for a verification that the intended orientation change has been performed can be achieved by utilizing an auxiliary measurement.

[0034] The present disclosure further relates to a computer program product comprising a non- transitory computer-readable storage medium having thereon a computer program comprising program instructions, the computer program being loadable into a processor and configured to cause the processor to perform the previously disclosed method.

[0035] The present disclosure further relates to a system for determining a relative position between a first platform and a second platform. The system comprises a first transducer, a first computer, and a first memory storage comprised in the first platform; and a second transducer, a second computer, and a second memory storage comprised in the second platform, wherein the first computer is arranged to

[0036] - transmit a request for a positional signal to the second platform, the second computer is arranged to

[0037] - receive the request for the positional signal; and

[0038] - determine and transmit a positional signal based on the received request, and the first computer is arranged to

[0039] - determine an orientation change over time for the first transducer;

[0040] - simultaneously measure the transmitted positional signal from the second platform with the first transducer, and perform the determined orientation change of the first transducer by controlling a motion control system of the first platform and / or by controlling an transducer orientation system arranged to change the orientation of at least part of the transducer; and

[0041] - calculate the relative position for the first platform and the second platform based on signal strength values of the measured positional signal, and the performed orientation change.

[0042] In some embodiments, the system comprises the first and second platforms.

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Fig. 1a-b shows schematically a system of two platforms each comprising an antenna arrangement.

[0045] Fig. 2 illustrates a platform comprising an antenna arrangement.

[0046] Fig. 3a-d illustrates the measurable positional signal strength measured by an antenna from an antenna arrangement.

[0047] Fig. 4 shows a method for determining a relative position between a first platform and a second platform.

[0048] Fig. 5 depicts schematically a data processing unit comprising a computer program product for providing a relative position between a first platform and a second platform.

[0049] DETAILED DESCRIPTION

[0050] Throughout the figures, same reference numerals refer to same parts, concepts, and / or elements. Consequently, what will be said regarding a reference numeral in one figure applies equally well to the same reference numeral in other figures unless explicitly stated otherwise. The term platform relates to a vehicle or a stationary structure. For example, the platform may be an aircraft, watercraft, landcraft, or electronic communication station.

[0051] The term transducer relates to a device that converts one type of energy into another. For example, a transducer may be an antenna arranged to convert between electrical signals and electromagnetic waves, or a sonar arrangement arranged to convert between electrical signals and material waves in a fluid.

[0052] The terms antenna array or antenna arrangement relates to a set of emitters, receivers and / or transceivers arranged to convert between electrical power and electromagnetic waves.

[0053] The term “directional antenna array” relates to devices arranged to receive and / or transmit signals in a radiation patterns in at least one lobe. The term lobe relates to the radiation pattern produced by an antenna or the detection pattern of the antenna, typically, a shape that represents the angles where the antenna ideally performs.

[0054] The expression “transmitting a radiation pattern” relates to emitting electromagnetic waves that distribute energy into space. Typically, transmitting a radiation pattern may be described or depicted in terms of power density or field strength versus angle.

[0055] The expression “radiation pattern for receiving signals” relates to detecting electromagnetic waves and the angular dependence of measured signal strength values.

[0056] The term radiation pattern metrics relates to values describing the properties of a lobe of an antenna’s radiation pattern. Typically, said metrics are known beforehand, or are estimated. Herein, the most relevant metric typically relates to the expected relative signal strength from a signal transmitted in and around each lobe, which may be utilized together with measurement values to calculate an angle towards the transmitter.

[0057] The term positional signal relates to a sustained transmission of a radiation pattern from a platform configured to be measured by another platform during a period of time. The term positional signal relates both to the radiation pattern shape and the signal information.

[0058] The expression “radiation pattern comprising two or more lobes” relates transmitting or detecting in a plurality of lobes that each have distinct characteristics in terms of angular separation and intensity. For determining a positional difference between platforms, the radiation pattern used is, typically, not an isotropic radiation pattern.

[0059] The term signal strength relates to a measurement of a part of a transmitted radiation pattern. Typically, signal strength is measured over time at a receiving antenna. Typically, a device arranged to measure signal strength comprises a calibrated field strength meter or other device arranged to help accurately compare the signal strength of different measurements.

[0060] The term “relative position” relates to a vector describing the difference in position between two positions, such as between the antenna arrangements of two platforms.

[0061] The term “distinguishable lobes” relates to a transmitted radiation pattern comprising lobes that are different and identifiable. Typically, distinguishable lobes relates to each lobe being unique in signal strength, wavelength, polarization, or transmitted information.

[0062] Fig. 1a-b shows schematically a system 100 of two platforms 101 ,102, wherein the first platform

[0063] 101 comprises an antenna arrangement arranged to measure signals in a radiation pattern corresponding to a lobe 110. The second platform 102 is transmitting a positional signal 120 to be measured by the first platform 101. It is to be understood that the size of the lobe of the antenna arrangement correspond to a detectable signal strength is, typically, significantly larger than the size of the platforms. The relative sizes of platforms and lobes shown in the figures are used for illustrative purposes.

[0064] Fig. 1a depicts the system 100 from a top-down view illustrating the lobe 110 of the radiation pattern of the antenna arrangement of the first platform. In this initial state the second platform

[0065] 102 is steadily transmitting the positional signal 120 that is detectable by the antenna arrangement of the first platform 101 .

[0066] It is to be understood that while lobes of radiation patterns, typically, represent a mathematical relationship between signal strength and angles of transmission or reception, the depiction of lobes in fig. 1a-b mainly serve to illustrate how a radiation pattern changes orientation relative to platforms. Herein, the depicted lobes 110 represent a volume inside which a signal source is readily detectable by the first platform 101 , wherein for a given distance from the antenna arrangement the measured signal strength is highest at the major axis of each lobe.

[0067] Fig. 1 b depicts the system 100 after the receiving antenna arrangement of the first platform 101 has been rotated while the second platform 102 still transmits the positional signal 120, thereby changing the position of the second platform 102 within said lobe 110 compared to fig. 1a. In the example of fig. 1a-b, the signal strength of the transmitted positional signal 120 measured by the antenna arrangement of the first platform 101 is different after the rotation. During the rotation of the antenna arrangement of the first platform 101 the changes in signal-strength values of the measured positional signal from the second platform 102 changed over time based on the rotation, the relative position between the platforms 101 ,102 and the radiation pattern of the receiving antenna. The rotation of the radiation pattern of the receiving antenna arrangement may be caused by the whole first platform 101 changing pose, by the antenna arrangement or parts thereof changing orientation in relation to the first platform 101 , and / or by the antenna arrangement redirecting the radiation pattern, such as in phased array antennas.

[0068] For embodiments with nimble flying platforms, such as a drone, a rapid change in radiation pattern orientation may typically be performed by changing the orientation of the flying platform itself, while for embodiments with large or stationary platforms, such as a ship or a station, a rapid change in radiation pattern orientation may typically be performed by changing the orientation of the antenna arrangement relative to the platform.

[0069] During the orientation change of the radiation pattern that occurred between the states corresponding to fig. 1a and fig. 1 b, the lobe 110 was swept over the second platform 102. Typically, the orientation change is arranged to occurs at a rate that allows the antenna arrangement of first platform 101 to measure a plurality of signal strength values for the positional signal 120 transmitted from the second platform 102 at different stages of orientation change.

[0070] In the examples, in fig. 1a-b at least the first platform 101 is a craft arranged to readily change orientation in order to change radiation pattern orientation, and the relative distance between the two platforms 102 is substantially the same in the two shown states.

[0071] It is further to be understood that a requirement for said lobe(s) of the radiation pattern of receiving antenna in order to be used for determining relative position is to have some angular dependence, that is to say, having at least some variation in radiation pattern based on the angle of detection.

[0072] In some examples, the second platform 102 comprises an antenna arrangements arranged to transmit the positional signal in a radiation pattern comprising a plurality of lobes (not shown), and the first platform 101 is arranged to measure signal strength values of any detected lobe of said radiation pattern.

[0073] It is to be understood that the radiation pattern may be utilized to transmit information on a format according to a wireless communication protocol used between said platforms 101 ,102. In some examples, the antenna arrangement of the first platform 101 is arranged to communicate wirelessly with the second platform 102. In some of these examples, the antenna arrangement is arranged to communicate wirelessly with the second platform 102 by transmission of a positional signal in said radiation patterns.

[0074] Fig. 1-3 describes embodiments of the invention utilizing antenna arranged to transmit and receive electromagnetic radiation. It is to be understood that the invention further relates to embodiments with other transducers, such as a sonar arrangement arranged to transmit and receive material waves. The transducer is arranged to transmit and / or receive the positional signal, and comprises the antenna arrangement and / or the sonar arrangement.

[0075] Fig. 2 shows a platform 101 ,102 comprising an antenna arrangement 210, a computer 220, and a memory storage 230. The antenna arrangement 210 and the memory storage 230 are connected to a computer 220.

[0076] The computer 220 is arranged to control the antenna arrangement 210 to transmit and / or receive a positional signal according to a radiation pattern.

[0077] In some examples, the platform comprises an antenna orientation system 240 arranged to change the orientation of the antenna arrangement, thus allowing change of orientation of the radiation pattern.

[0078] In some examples, the computer 220 is arranged to control the antenna arrangement 210 and / or the antenna orientation system 240.

[0079] In some examples, the platform 101 , 102 comprises a motion control system 260, wherein the motion control system 260 is arranged to change the orientation of the platform 101 ,102 to cause a change in orientation of any radiation pattern, whereby the radiation pattern corresponding to receiving and / or transmitting a positional signal changes pose. In some examples, the platform 101 , 102 comprises a navigation system 250 connected to the computer 220 and the motion control system 260, wherein the navigation system 250 is arranged to communicate with the computer 220 and control the motion control system 260. For example, the navigation system 250 and motion control system 260 may be core systems of the platform 101 ,102 as such, while the antenna arrangement 210, computer 220 and memory storage 230 may together constitute an ancillary system that is in communication with the navigation system 250 of the platform 101 ,102.

[0080] In some examples, the navigation system 250 is arranged to determine a bearing of the platform 101 , 102.

[0081] In some examples, the memory storage 230 comprises data indicative of the radiation patterns produced by the antenna arrangement 210, such as signal strength profiles for lobes. In some examples, the memory storage 230 comprises data indicative of the radiation patterns expected to be transmitted by the antenna arrangement 210 of other platforms 101 ,102. In some examples, the computer 220 is arranged to send and / or receive data indicative of the radiation patterns, and retrieve and / or store said data on the memory storage 230. In some examples, the computer 220 is arranged to store data indicative of a performed transmission of the positional signal in a radiation pattern and / or the orientation change performed by a receiving antenna of a platform 101 ,102 during said transmission on the memory storage 230. In some examples, the computer 220 is arranged to communicate data indicative of a performed transmission of a radiation pattern and / or the orientation change performed during said transmission to another platform 101 ,102. In some of these examples, the computer 220 is arranged to determine a bearing relating to the own platform and communicate said determined bearing.

[0082] It is to be understood that “data indicative orientation change performed during said transmission” may comprise information of the orientation change of the antenna arrangement 210 and / or the orientation change of the platform 101 ,102. In some examples, said data indicative orientation change comprises a relation to a determined bearing or a cardinal direction.

[0083] In some examples, the computer 220 is arranged to transmit and / or receive data indicative of the radiation pattern transmitted by the antenna arrangement 210.

[0084] In some examples, the computer 220 is arranged to obtain radiation pattern metrics relating to values describing the properties of the radiation pattern of the receiving antenna arrangement, and the computer 220 is arranged to calculate the relative position based on said radiation pattern metrics. In some of these examples, the memory storage 230 is arranged to store and provide said radiation pattern metrics. In some of these examples, said radiation pattern metrics relates to values describing the properties of the radiation pattern of the transmitting antenna arrangement. Typically, said metrics are known beforehand, or are estimated.

[0085] In some examples, the computer 220 is arranged to store data indicative of the lobes produced by the antenna arrangement 210 in the memory storage 230. In some of these examples, the computer 220 is arranged to calibrate the lobe shape(s) for the transmitted positional signal based on navigation data, received request for a positional signal, and / or received data indicative of signal-strength values of the measured positional signal of at least one transmitted radiation pattern. Typically, calibration is performed in situations when additional navigation options are available to determine navigation data, such as GPS, an inertial measuring unit, IMU, or an inertial navigation system, INS, that has recently been corrected. In some of these examples, the computer 220 is arranged to calibrate the lobe shape(s) based on information indicative of a measured radiation pattern received from another platform 101 ,102.

[0086] In some examples, the computer 220 is connected to and / or comprises a high precision clock (not shown). In some of these examples, the computer 220 is arranged to calculate a distance to another platform based on time-of-flight of transmissions by utilizing the high precision clocks in each platform.

[0087] In some examples, the antenna arrangement 210 comprises a directional antenna array arranged to focus transmission and / or detection in a specific direction.

[0088] Fig. 3a-d illustrates the changes in signal strength detected from signal sources at different positions in the lobe 110 of a radiation pattern of a detecting antenna of an antenna arrangement. Fig. 3a illustrates the lobe of a receiving antenna of a platform 101 and fig. 3b shows a plot schematically depicting the measured signal strength for a signal source positioned along a path through the lobe 110. Fig. 3c illustrates an antenna lobe 110 of a first platform 101 changing orientation while measuring a positional signal 120 transmitted from a second platform 102, whereby the lobe 110 sweeps over the second platform 102. Fig. 3d shows a plot depicting the signal strength measured by the first platform 102 corresponding to the orientation change in fig. 3c.

[0089] It is to be understood that the lobe shapes and signal strength values shown are for illustrative purposes and may not match experimental data for radiation patterns transmitted from antenna arrangements as a function of relative pose.

[0090] Fig. 3a illustrates the lobe 110 from the antenna arrangement of the platform 101 with a radiation pattern that corresponds to the angular dependence of signal-strength values of a measured positional signal. A path, A-A, through the lobe 110 goes straight through the major axis of the lobe 110. Fig. 3b shows a plot with a curve 115 representing the measured signal strength for a constantly transmitting source positioned along the path A-A. The signal strength curves and shape of the lobe, such as corresponding to fig. 3a-b, may be predetermined and stored on a memory storage, for use as a reference for determining relative positions 140. Correspondingly, a 3D representation of the signal strength of the lobe of the radiation pattern may be predetermined and stored on a memory storage. The information represented in fig. 3b may be viewed as the known property of the radiation pattern.

[0091] It is to be understood that the shape and signal strength of radiation patterns and their lobes may be different for a plurality of different detection modes of the antenna, and predetermined information describing said radiation patterns for said plurality of different detection modes may be stored on a memory storage at the transmitting platform 101 and / or the receiving platform 102.

[0092] Fig. 3c illustrates the lobe 110 from the first platform 101 measuring transmitted positional signal 120 from a second platform 102, while the first platform 110 is changing orientation by rotating in the plane. The second platform 102 is, at the start of transmission and measurement, inside the lobe 110 of the first platform 101 . As the first platform 101 rotates the lobe 110 sweeps over the second platform 102. Fig. 3c further indicates the sought relative position vector 140 that corresponds to the difference in position between the platforms 101 ,102. In the scenario relating to fig. 3c-d, the relative velocity between the first platform 101 and second platform 102 is significantly smaller than the tangential velocity of the lobe 110 sweeping over the second platform 102. For most situations the tangential velocity is expected to be significantly larger than the rate of change in relative position between platforms 101 ,102, however, in embodiments where the rate of change in relative position between platforms 101 ,102 may impact calculations then velocity and bearing information may be communicated between platforms in order to compensate for relative movement during transmissions.

[0093] Fig. 3d shows a plot with a curve 116 representing signal-strength values of the measured positional signal at the first platform 101 as the first platform 101 changes orientation by rotating at a continuous rate, with the measurement of the transmitted positional signal 120 starting at to and ending at IEND. The time to corresponds to the state shown in fig. 3c, followed by a continuous rotation until IEND. Typically, the duration of the measurement of the radiation pattern is substantially the same as the duration of the transmission of said radiation pattern, as typically the transmitted positional signal 120 has been transmitted after a requested from the first platform 101. The dotted line, before to, relates to non-measured signal strength assuming a continuous rotation before to, and herein only serves as a visual guide to more clearly show the relationship between the measured radiation pattern in fig. 3d with the signal strength curve in fig. 3b.

[0094] By combining the measured signal strength and the orientation change over time, a comparison may be made with a representation of the signal strength of the lobe of the radiation pattern, such as shown in figure 3b, in order to calculate where in the lobe, or at what angle, the second platform was located.

[0095] It is to be understood that a predetermined information corresponding to measured signal strength values for signal sources located throughout the radiation pattern for the antenna arrangement, such as shown in fig. 3b, may be used to calculate a relative position 140 to the second platform 102. This may be performed by comparison with the curve of the signal strength over time measured at the first platform 101 during the sweep of the lobe 110 of the radiation pattern during the orientation change of the fist platform 101 , corresponding to fig. 3d. In order for a platform 101 ,102 to calculate the relative position 140 the platform needs to measure the transmitted positional signal 120, retrieve from memory and / or determine information relating to the radiation pattern properties and orientation change, and determine the measured signal strength. Additional information relating to the platforms, such as an estimated distance, an estimated bearing, and / or a velocity during transmission, may be utilized to improve the calculations of the relative position 140 and / or to reduce the computational cost. In some embodiments, utilizing a determined estimated distance between platforms may be needed to calculate a relative position 140 with acceptable uncertainty values.

[0096] In some examples, calculating the relative position 140 comprises combining

[0097] - information indicative of the measured positional signal relating to signal strength over time, and

[0098] - information indicative of the performed orientation change over time, to form a matching curve relating to signal strength as a function of orientation for the performed orientation change, and wherein said matching curve is compared to corresponding predetermined radiation pattern metrics relating to the positional signal to calculate the relative position.

[0099] In some of these examples, wherein an estimated distance between platforms has been determined, the matching curve comparison is further based on the estimated distance between the platforms.

[0100] Different approaches for matching the measured signal strength and a representation of the signal strength of the lobe of the radiation pattern, such as show in fig. 3b, may be performed depend on the number of measured of signal strength performed during the orientation change. The representations of the signal strength of the lobe of the radiation pattern may comprise 3D or 2.5D digital models of said signals and radiation patterns.

[0101] Fig. 4 shows a method for determining a relative position between a first platform and a second platform.

[0102] The method 300 for calculating the relative position between a first platform and a second platform, the method comprises

[0103] - establishing 310 a communication link between the first platform and the second platform,

[0104] - transmitting 311 a request for a positional signal from the first platform to the second platform,

[0105] - transmitting 320 a positional signal from the second platform utilizing an antenna arrangement;

[0106] - determining 330, using a computer comprised in the first platform, an orientation change over time for the antenna arrangement of the first platform,

[0107] - simultaneously measuring 350 the transmitted positional signal from the second platform with the antenna arrangement of the first platform, and performing the determined orientation change of the antenna arrangement;

[0108] - calculating 370, by one or more computers, the relative position for the first platform and the second platform based on information indicative of the measured transmitted positional signal and measured signal strength values, and the performed orientation change.

[0109] It is to be understood that “positional signal” in the expression “a request for a positional signal” may relate to any suitable signal being requested, therefore indefinite article is use in the subsequent step of “transmitting 320 a positional signal”. That is to say, the “request for a positional signal” is not limited to requesting one specific positional signal.

[0110] In some examples, establishing 310 the communication link between the first platform and the second platform further comprises determining an estimated distance between the first and second platforms, such as by utilizing time-of-flight, and wherein calculating the relative position is further based on said determined estimated distance.

[0111] The expression “by one or more computers” in the step of calculating 370 the relative position is to be interpreted broadly. It is to be understood that the step of calculating 370 the relative position may be performed in the first platform, in the second platform, in another platform able to communicate with the first platform and perform the calculations, or in a combination thereof. Typically, the step of calculating 370 the relative position is performed by the computer comprised in the first platform. In order to perform the calculation at any other platform, information indicative of the measured positional signal needs to be communicated from the first platform to said other platform(s). In some examples, the computer comprised in the first platform and / or a computer in the second platform is used for calculating 370 the relative position.

[0112] In some examples, transmitting 311 a request for a positional signal from the first platform to the second platform, and / or transmitting 320 a positional signal from the second platform, further comprises determining an estimated distance between the first and second platforms, such as by utilizing time-of-flight, and wherein calculating the relative position is further based on said determined estimated distance.

[0113] In some examples, utilizing time-of-flight comprises one platform sending a 1st timestamp corresponding to a time of sending, followed by the other platform sending the 1st, 2ndand 3rdtimestamps, wherein the 2ndand 3rdtimestamps correspond to time of receiving and sending of the other platform, wherein a 4thtimestamp is determined upon receiving the 1st, 2ndand 3rdtimestamps, and a distance is determined based on said timestamps. The creation of four timestamps, instead of only two, allows for elimination of drift between clocks and further allows for synchronization between the clocks of the platforms.

[0114] In some of these examples, the other platform sends a difference between the 1stand 2ndtimestamp, instead of sending the timestamps as such. In some examples, the other vehicle only sends information indicative of the 1stand 2ndtimestamp, or only sends information indicative of the 3rdtimestamp.

[0115] It is to be understood that there exists several different schemes for determining distance based on time-of-flight. Different approaches may be selected based on the capabilities of the platforms involved, and the requirements for accuracy and precision.

[0116] In some examples, calculating 370 the relative positional is based on obtaining predetermined information indicative of the signal strength during transmission of the transmitted positional signal. In some of these examples, the predetermined information is indicative of the signal strength during transmission being constant and / or following a predetermined pattern. In some of these examples, said predetermined information indicative of the signal strength during transmission is obtained from a memory storage of the first platform.

[0117] In some examples, the calculating 370 the relative position comprises providing the calculated relative position to a navigation system of the platform, and / or presenting the calculated relative position to a user.

[0118] In some examples, the method further comprises communicating 380 the calculated relative position from the first platform to the second platform.

[0119] In some examples, the method 300 comprises performing 360 at least one additional iteration of simultaneously measuring 350 the transmitted positional signal from the second platform and performing a different orientation change of the antenna arrangement, wherein calculating 370 the relative position between the first platform and the second platform is further based on information indicative of said radiation pattern and determined signal strength values for the additional iteration(s). In some of these examples, iterating 360 comprises determining 330, using computer, a corresponding orientation change over time for the antenna arrangement of the first platform.

[0120] Typically, performing an additional iteration comprises performing a different orientation change, such an initially performing an orientation change in the horizontal plane and then performing an orientation change with a significant vertical component.

[0121] In some examples, calculating 370 the relative position between the first platform and the second platform comprises determining a relative pose difference between the first platform and the second platform.

[0122] In some examples, iterating 360 comprises transmitting 311 request for a corresponding positional signal transmission from the first platform to the second platform. It is to be understood that a request for a corresponding positional signal transmission may not be needed if, at the time of initiating the iteration 360, the currently transmitted 320 positional signal from the second platform is expected to continue for long enough to allow for at least one measurement and orientation change to be performed. Typically, the first platform will have or receive information regarding the duration of the transmitted positional signal from the second platform.

[0123] In some examples, the method comprises determining the remaining duration of the transmitted positional signal from the second platform based on predetermined data, the established communication link, from the request for positional signal, and / or information from measurement of the positional signal. In some of these examples, transmitting 311 request for the positional signal transmission, and / or determining 330 the orientation change over time, and / or performing 360 at least one additional iteration is based on said determined remaining duration.

[0124] In some examples, establishing 310 the communication link comprises establishing a wireless communication protocol between the first platform and the second platform utilizing wireless communication devices.

[0125] In some examples, the wireless communication device of the first platform comprises the antenna arrangement. In some examples, the antenna arrangement is arranged to transmit said positional signal, and communicate with other platforms. In some examples, said positional signal further serves as a communication transmission.

[0126] In some examples, transmitting 320 a positional signal comprises determining the positional signal to be transmitted. In some examples, determining the positional signal to be transmitted is based on predetermined data, and / or the request for a positional signal from the first platform.

[0127] In some examples, the communication protocol comprises transmitting information via the positional signal. For example, the positional signal from the second platform may comprise at least some information indicative of the duration of the positional signal, and / or the type of positional signal being transmitted. In some examples, the first and second platform comprise information for a set of predetermined positional signals, and the positional signal comprises information indicative of which of the set of predetermined positional signals is being transmitted, preferably said information is comprised early in the transmission. In some of these examples, the positional signal comprises information indicative of an identifier corresponding to a positional signal of the set of predetermined positional signals.

[0128] In some examples, the transmitted positional signal is based on the request for a positional signal from the first platform. In some of these examples, the request for a positional signal from the first platform comprises information indicative of a positional signal of the set of predetermined positional signals.

[0129] In some examples, the positional signal comprises information with timestamps. In some of these examples, transmitting 320 a positional signal from the second platform and measuring 350 the transmitted positional signal at the first platform is performed utilizing high precision clocks. It is to be understood that in order to fully utilized the timestamp of a positional signal, such as estimating a distance between platforms, then each involved platform typically requires a high precision clock or an equivalent timekeeper.

[0130] In some examples, transmitting the positional signal comprises transmitting a radiation pattern comprising a plurality of lobes from the second platform. In some of these examples, each lobe comprises lobe ID information, wherein the lobe ID information serves to make the lobe distinguishable. In some of these examples, information indicative of said lobe ID is predetermined and stored in memory storage of each platform. It is to be understood that identifiers for lobes of positional signal radiation patterns may be established beforehand between all platforms.

[0131] In some examples, request for a positional signal comprises a request for the positional signal to comprise a radiation pattern with a plurality of lobes. In some examples, the request for positional signal comprises a request for relative orientation of the radiation pattern of the positional signal, such as three lobes spread in the horizontal plane.

[0132] In some examples, transmitting the positional signal from the second platform is performed across a time period of at least 10 ms. In some of these examples, transmission is performed for at least 40 ms, at least 80 ms, at least 150 ms, at least 300 ms, at least 500 ms, at least 1 000 ms, at least 2 000 ms, at least 4 000 ms, or at least 10 000 ms.

[0133] In some examples, measuring 350 the positional signal at the first platform comprises determining the signal strength value for at least two, or at least three, points in time across a time period of at least 10 ms. In some of these examples, signal strength values are determined across at least 40 ms, at least 80 ms, at least 150 ms, at least 300 ms, at least 500 ms, at least 1 000 ms, at least 2 000 ms, at least 4 000 ms, or at least 10 000 ms.

[0134] In some examples, measuring 350 the positional signal at the first platform comprises determining the signal strength value for at least three points in time. In some of these examples, the number of signal strength values determined at different times is at least five, at least ten, at least twenty, or at least one hundred. In some examples, measuring 350 the positional signal at the first platform comprises determining the signal strength values based on a predetermined minimum sampling rate. In some of these examples, the predetermined minimum sampling rate is based on the expected orientation change per unit time of the first platform, such as the first platform being a drone with a known turn rate.

[0135] In some examples, the predetermined minimum sampling rate is at least 1 Hz. In some of these examples, the predetermined minimum sampling rate is at least 2 Hz, at least 5 Hz, at least 10 Hz, at least 30 Hz, or at least 100 Hz.

[0136] In some examples, measuring 350 the positional signal at the first platform comprises determining the signal strength values based on a predetermined minimum sampling rate per unit of angular displacement.

[0137] It is to be understood that the mentioned minimum sampling rates are exemplary and not limiting.

[0138] In some examples, establishing 310 the communication link between the first platform and the second platform comprises determining an estimated distance between the platforms, and / or an estimated bearing between the first platform and the second platform. In some examples, calculating 370 the relative position is based on said estimated distance and / or estimated bearing.

[0139] In some examples, measuring 350 the positional signal at the first platform comprises determining the signal strength values based on a predetermined minimum sampling rate based on the estimated distance between the first platform and the second platform.

[0140] In some examples, wherein the positional signal from the second platform comprises a radiation pattern comprising a plurality of lobes, measuring 350 the transmitted positional signal comprises determining the lobe having the highest measured signal strength among detected lobes. In some of these examples, calculating 370 the relative position is based on the measured signal strength for the lobe with the highest measured signal strength.

[0141] In some examples, performing 360 at least one additional iteration of simultaneously measuring 350 the transmitted positional signal from the second platform and performing a different orientation change of the antenna arrangement is based on the lobe with the highest measured signal strength, such as the corresponding request for the positional signal comprising an instruction to transmit 320 a corresponding positional signal based on the lobe with the highest measured signal strength.

[0142] In some examples, determining 330 the orientation change over time for the antenna arrangement of the first platform comprises determining an orientation change for the first platform and / or antenna arrangement to be performed based on the information indicative of the measured positional signal. In some of these examples, the antenna orientation system is controlled based on the received information indicative of the measured positional signal, and / or a motion control system of the platform is controlled based on he received information indicative of the measured positional signal. In some examples, the motion control system comprises a propulsion system for the platform.

[0143] In some example, measuring 350 the transmitted positional signal with the antenna arrangement comprises measuring the positional signal utilizing a plurality of measurement lobes. In some of these examples, measuring 350 the transmitted positional signal utilizes a radiation pattern comprising a plurality of lobes, wherein each lobe is selected to be in a direction expected to at least partially overlap the second platform upon performing the determined orientation change.

[0144] In some examples, transmitting 350 the positional signal and performing the determined orientation change comprises measuring the orientation change of the first platform and / or the antenna arrangement. In some of these examples, measuring the orientation change is performed utilizing an inertial measurement unit, IMU, and / or an inertial navigation system, INS. It is to be understood that measuring the orientation of the platform or antenna arrangement may further allow for an improved execution of the orientation change, and may also provide a more accurate information indicative of the performed orientation change, thus improving calculating 380 the relative position. In some examples, the orientation change is estimated based on the actions taken to perform the orientation change, such as the activation of the propulsion system of a drone during a turn. In some examples, calculating 370 the relative position is based on said measured and / or estimated orientation change.

[0145] Fig. 5 depicts schematically a data processing unit comprising a computer program product for calculating the relative position between a first platform and a second platform. Fig. 5 depicts a data processing unit 410 comprising a computer program product comprising a non-transitory computer-readable storage medium 412. The non-transitory computer-readable storage medium 412 having thereon a computer program comprising program instructions. The computer program is loadable into a data processing unit 410 and is configured to cause a processor 411 to carry out the method.

[0146] Returning to fig. 1a-b depicting a system 100 of two platforms 101 ,102, and fig. 2 depicting an antenna arrangement comprised in a platform 101 ,102.

[0147] The present disclosure further relates to a system for determining a relative position between a first platform 101 and a second platform 102. The system 100 comprises a first antenna arrangement 210, a first computer 220, and a first memory storage 230 comprised in the first platform 101 ; and a second antenna arrangement 210, a second computer 220, and a second memory storage 230 comprised in the second platform 102. The first computer 220 is arranged to

[0148] - transmit a request for a positional signal to the second platform 102.

[0149] The second computer 220 is arranged to

[0150] - receive the request for the positional signal; and

[0151] - determine and transmit 320 a positional signal based on the received request.

[0152] The first computer 220 is arranged to

[0153] - determine an orientation change over time for the antenna arrangement 210;

[0154] - simultaneously measure the transmitted positional signal from the second platform with the antenna arrangement 210, and perform the determined orientation change of the antenna arrangement 210 by controlling a motion control system 260 of the first platform 101 and / or by controlling an antenna orientation system 240 arranged to change the orientation of at least part of the antenna arrangement 210;

[0155] - calculate the relative position for the first platform and the second platform based on signal strength values of the measured positional signal, and the performed orientation change.

[0156] It is to be understood that “performing the determined orientation change of the antenna arrangement 210 by controlling a motion control system of the first platform 260” is not limited to the computer 220 directly controlling the motion control system. For example, the computer 220 may communicate with a navigation system 250 of the first platform 101 that in turn controls the motion control system 260.

[0157] It is to be understood that when the term transducer replaces the term antenna arrangement, then the antenna orientation system 240 is replaced with a transducer orientation system 240. Correspondingly, for embodiments utilizing a sonar arrangement as a transducer, the term sonar orientation system 240 is used.

[0158] In some examples, the computer 220 is arranged to receive information indicative of the performed orientation change of the antenna arrangement 210 from the navigation system 250 and / or the motion control system 260 of the first platform 101. In some of these examples, calculating the relative position is based on said received information indicative of the performed orientation change.

[0159] The first computer 220 is arranged to calculate the relative position for the first platform and the second platform based on information indicative of the measured transmitted positional signal and measured signal strength values, and the performed orientation change.

[0160] In some of these examples, the first computer 220 is arranged to calculate the relative position based on obtained data indicative of the properties of transmitted positional signal, such as the positional signal being transmitted at a predetermined signal intensity. In some examples, the second computer 220 is arranged to transmit the positional signal at a constant signal intensity, and the first computer 220 is arranged to obtain data indicative of the positional signal being transmitted at a constant signal intensity, and calculate the relative position based on the data indicative of constant signal intensity.

[0161] It is to be understood that the first platform 101 and the second platform 102 may comprise data indicative of one or more predetermined positional signal properties relating to the positional signals being transmitted by the second platform 102. It is to be understood that the intensity of the transmitted positional signal may vary over time in intensity or the shape of the transmission pattern, and that the first computer 220 may be arranged to predict and / or identify the positional signal being measured. The first computer 220 may be arranged to calculate the relative position based on said data indicative of one or more predetermined positional signal properties

[0162] In some examples, each platform 101 ,102 comprises a communication system arranged to establish a communication link between the first platform 101 and the second platform 102. In some examples, the communication system comprises the antenna arrangement 210 and / or the computer 220. In some examples, the antenna arrangement 210 and the computer 220 functions as the communication system.

[0163] In some examples, a 3D representation of the signal strength of the lobe(s) of the positional may be predetermined and stored on each memory storage 230. In some examples, properties for a set of positional signals are stored on at least one memory storage 230. It is to be understood that properties of the transmitted positional signal may be received via communication with the other platform 101 ,102 and / or retrieved from the memory storage 230. In some examples, the request for a positional signal describes properties of the positional signal to be transmitted, such as a duration and / or radiation pattern shape of the positional signal. For examples, the first platform 101 may request a positional signal with a duration long enough to allow for performing two different orientation changes, such as a substantially vertical rotation and a substantially horizontal rotation.

[0164] In some examples, the system comprises the first platform 101 and / or the second platform 102.

[0165] In some example, the first platform 101 and / or the second platform 102 each comprise a motion control system 260. In some examples, the motion control system 260 comprises a propulsion system and / or an orientation control system. In some of these examples, the computer is arranged to directly or indirectly control the motion control system 260 of the first platform 101 and / or the second platform 102. In some examples, the antenna arrangement 210 comprises a field strength meter arranged to measure signal strength values. The use of a field strength meter allows for more reliable measurements of the positional signal and the signal strength values measured.

[0166] In some examples, the first computer 220 is arranged to

[0167] - measure the transmitted positional signal utilizing a plurality of lobes, and determine the lobe with the strongest signal based on the measured positional signal, and wherein the first computer 220 is arranged to

[0168] - transmit an additional request for a positional signal to the second platform, wherein the request is based on the determine lobe with the strongest signal, and / or

[0169] - measure the transmitted positional based on the determine lobe with the strongest signal, such as initially orienting the poles of the antenna arrangement 210 and / or determining the orientation change in order to match the sweep of the determine lobe with the strongest signal.

[0170] It is to be understood that the determined lobe with the strongest signal based on the measured positional signal is indicative of an approximate bearing towards the second platform 102.

[0171] Additional information relating to the platforms 101 ,102, such as an estimated distance, an estimated bearing, and / or a velocity during transmission, may be utilized by the system 100 to improve the calculations of the relative position and / or to reduce the computational cost.

[0172] In some examples, each computer 220 is connected to and / or comprises a high precision clock (not shown). In some of these examples, at least one computer 220 is arranged to calculate a distance to the other platform based on time-of-flight of transmissions by utilizing the high precision clocks in communication.

[0173] In some examples, the second computer 220 is arranged to transmit information indicative of velocity and / or bearing information for the second platform 102 to the first platform 101. In some examples, the first computer 220 is arranged to determine a rate of change of position between the platforms during transmission of the positional signal based on communicated velocity and / or bearing information, wherein the computer is arranged to calculate the relative position further based on the determine a rate of change of position and / or a determined distance between the platforms.

[0174] In some examples, the second computer 220 is arranged to, upon determine and transmit 320 a positional signal based on the received request, include information indicative of the duration of the positional signal and / or information indicative of the radiation intensity of the positional signal, such as the wattage per steradian.

Claims

CLAIMS1 . Method for determining a relative position between a first platform and a second platform, the method (300) comprises- establishing (310) a communication link between the first platform (101 ) and the second platform (102);- transmitting (311 ) a request for a positional signal from the first platform (101 ) to the second platform (102);- transmitting (320) a positional signal from the second platform (102) utilizing a transducer, wherein the positional signal has a radiation pattern comprising at least one lobe;- determining (330), using a computer (220) comprised in the first platform (101 ), an orientation change over time for a transducer of the first platform (101 );- simultaneously measuring (350) the transmitted positional signal from the second platform (102) with the transducer of the first platform (101 ), and performing the determined orientation change of the transducer by controlling a motion control system (260) of the first platform (101 ) and / or by controlling a transducer orientation system (240); and- calculating (370), by one or more computers, the relative position (140) for the first platform (101 ) and the second platform (102) based on the signal-strength values of the measured positional signal, and the performed orientation change.

2. The method according to claim 1 , wherein the transducer comprises an antenna arrangement (210) and / or a sonar arrangement.

3. The method according to claim 1 or 2, wherein the first platform and / or the second platform is an aircraft, landcraft, and / or watercraft.

4. The method according to any preceding claim, wherein the measurement of the positional signal and the corresponding orientation change of the transducer occurs over at least 100 ms.

5. The method according to any preceding claim, wherein establishing (310) the communication link comprises determining an estimated distance between the platforms (101 ,102) based on time-of-flight, and wherein calculating (370) the relative position (140) is further based on said determined estimated distance.

6. The method according to claim 5, wherein the estimated distance between the platforms is determined using timestamped transmissions and precise clocks comprised in each platform, and utilizing time-of-flight to estimate the distance.

7. The method according to any preceding claim, wherein calculating (370) the relative position (140) comprises combining- information indicative of signal-strength values of the measured positional signal over time, and- information indicative of the performed orientation change over time, to form a matching curve relating to signal strength as a function of orientation for the performed orientation change, and wherein said matching curve is compared to corresponding predetermined radiation pattern metrics relating to the positional signal to calculate the relative position (140).

8. The method according to claim 7, further comprising the features of claim 5 or 6, wherein the matching curve comparison is further based on the estimated distance between the platforms.

9. The method according to any preceding claim, wherein the method (300) comprises performing (360) at least one additional iteration of simultaneously measuring (350) the transmitted positional signal from the second platform and performing a different orientation change of the transducer, wherein calculating (370) the relative position (140) between the first platform (101 ) and the second platform (102) is further based on information indicative of said radiation pattern and determined signal strength values for said at least one additional iteration.

10. The method according to any preceding claim, wherein the step of transmitting (320) the positional signal comprises determining at least one timestamp, platform ID, and / or lobe ID, and wherein- measuring (350) comprises determining said at least one timestamp, platform ID, and / or lobe ID, and- calculating (370) the relative position (140) is based on said determined at least one timestamp, platform ID, and / or lobe ID.

11. The method according to any preceding claim, wherein the first platform (101 ) is a mobile platform and the orientation change is performed at least in part by an orientation change of said first platform (101 ), and wherein, during measuring (350) of the positional signal, information indicative of the orientation change performed is determined utilizing an IMU and / or an INS comprised in the first platform (101 ).

12. A computer program product comprising a non-transitory computer-readable storage medium (412) having thereon a computer program comprising program instructions, the computer program being loadable into a processor (411 ) and configured to cause the processor (411 ) to perform the method (300) for determining a relative position between a first platform and a second platform according to any one of the preceding claims.

13. System for determining a relative position between a first platform and a second platform, the system comprises a first transducer, a first computer (220), and a first memory storage (230) comprised in the first platform (101 ); and a second transducer, a second computer (220), and a second memory storage (230) comprised in the second platform (102), wherein the first computer (220) is arranged to- transmit a request for a positional signal to the second platform (102), the second computer (220) is arranged to- receive the request for the positional signal; and- determine and transmit (320) a positional signal based on the received request, and the first computer (220) is arranged to- determine an orientation change over time for the first transducer;- simultaneously measure the transmitted positional signal from the second platform with the first transducer, and perform the determined orientation change of the first transducer by controlling a motion control system (260) of the first platform (101 ) and / or by controlling a transducer orientation system (240) arranged to change the orientation of at least part of the transducer; and- calculate the relative position (140) for the first platform and the second platform based on signal strength values of the measured positional signal, and the performed orientation change.

14. The system according to claim 13, wherein the system comprises the first and second platforms (101 ,102).

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