Patent Description:
The automated navigation of unmanned aerial vehicles (UAV) at low altitudes in the so-called urban "Low-Speed Localized Traffic" area [<NPL>], requires an adequate unmanned aerial vehicles traffic management (UTM) system. The major concern of such a system is safe maneuvering of UAVs in an urban environment, without causing any harm or danger. Another concern is cost-efficient implementation of such a system, while being reliable.

A constant and dependable communication link between the UAVs in the field and the UAV command center is also needed, in order to maintain control of the entire UAV fleet.

Different from UAV flight paths above houses, flight paths between high buildings in narrow street canyons near the ground level of dense urban environments have limited coverage of positioning satellite. Therefore, such a system may not depend on global navigation satellite system (GNSS) satellite positioning. This applies even more for navigation of automated UAV flights in an indoor environment.

An additional problem is inherent to satellite positioning systems: GNSS is vulnerable to jamming or spoofing [<NPL>], which can lead to hazardous situations.

In order to navigate UAVs without GNSS, [<NPL>] proposes an "optical flow navigation", which is a technique used to determine the motion of objects in relation to the observer. This proposal requires camera sensors and adequate data processing algorithms installed in the UAV, which increases the complexity and cost of UAVs. Furthermore, this approach is not able to ensure that the UAV follows a predefined airway.

"A microwave landing system (MLS) is an all-weather, precision landing system, which has a number of operational advantages, including a wide selection of channels to avoid interference with other nearby airports, excellent performance in all weather, a small "footprint" at the airports, and wide vertical and horizontal "capture" angles that allowed approaches from wider areas around the airport" [https://en. org/wiki/Microwave_landing_system].

"The Microwave Scanning Beam Landing System (MSBLS) is a Ku band approach and landing navigation aid formerly used by NASA's space shuttle. It provides precise elevation, directional and distance data which was used to guide the orbiter for the last two minutes of flight until touchdown" [https://en. org/wiki/Microwave_Scanning_Beam_Landing_System].

<FIG> shows an illustrative view of an instrument landing system (ILS) and a beam pattern used by the ILS. As shown in <FIG>, the ILS uses a transmit (Tx) station transmitting partially overlapping left and right beams, e.g., at <NUM> and <NUM>, respectively. An aerial vehicle will follow an overlap path of the left and right beams along which the received powers of the left and right beams are equal. In other words, <FIG> shows an operation of navigation system on the left and a numerically generated beam pattern from lens and beam cross-section measurements on the right.

A High-Precision Millimeter-Wave Navigation System for Indoor and Urban Environment Autonomous Vehicles is proposed in [<NPL>]. The system is suitable for applications where precision guiding of small autonomous vehicles along a precise path is required such as navigating indoors or in cluttered urban environments.

The solutions provided in [https://en. org/wiki/Microwave_landing_system], [https://en. org/wiki/Microwave_Scanning_Beam_Landing_System] and [<NPL>] enable precise landing procedures for UAVs, but are not suitable for an UAV airway system. This requires that the UAV not only estimates the source of the signal in order to adjust its flight path accordingly, but instead an adequate UAV airway system has to allow for precise position estimates along the designated airway path, hence the position in the three-dimensional space.

Another problem of the above solution is its vulnerability to multipath, which occurs frequently in indoor environments.

<CIT> discloses a delivery system having unmanned aerial delivery vehicles and a logistics network for control and monitoring. A ground station provides a location for interfacing between the delivery vehicles, packages carried by the vehicles and users. The delivery vehicles autonomously navigate from one ground station to another. The ground stations provide navigational aids that help the delivery vehicles locate the position of the ground station with increased accuracy.

<CIT> discloses a unitary, integrated navigation instrument in which RF receiving and sampling operations and hyperbolic coordinate conversion operations are provided by time-sharing functional component groupings forming a sampler stage, an arithmetic unit, a memory, and a detector and sequential decoder section with a basic RF tuning unit and with each other through the operation of a control unit including timing and priority circuits, to form an instrument which does not have a separate receiver and a computer-converter, but which nonetheless performs the functions of both.

Therefore, it is the object of the present invention to provide a concept that improves positioning of unmanned aerial vehicles in dense urban environments.

This object is solved by the independent claims.

Advantageous implementations are addressed in the dependent claims.

Embodiments provide an unmanned aerial vehicle comprising a receiver and a position determiner. The receiver is configured to receive two periodic wideband signals transmitted from two spaced apart base stations of a navigation system for unmanned aerial vehicles, wherein the two periodic wideband signals are time-synchronized. The position determiner is configured to determine a position of the unmanned aerial vehicle relative to the two base stations based on a difference between reception times of the two periodic wideband signals and based on reception intensities of the two periodic wideband signals, wherein the unmanned aerial vehicle is configured to fly along a flight path defined by beams using which the two wideband signals are transmitted by the two base stations, wherein the beams face and overlap each other thereby defining the flight path for the unmanned aerial vehicle.

Further embodiments provide a navigation system for unmanned aerial vehicles, the navigation system comprising two spaced apart base stations configured to transmit two time-synchronized periodic wideband signals, wherein the two spaced apart base stations are adapted to transmit the two periodic wideband signals using beams, wherein the beams face and overlap each other thereby defining a flight path for an unmanned aerial vehicle.

Further embodiments provide a method, the method comprising a step of transmitting two time-synchronized periodic wideband signals from two spaced apart base stations; a step of receiving the two periodic wideband signals at the unmanned aerial vehicle; and a step of determining a position of the unmanned aerial vehicle relative to the two spaced apart positions based on a difference between reception times of the two periodic wideband signals and based on reception intensities of the two periodic wideband signals, flying with the unmanned aerial vehicle along a flight path defined by beams using which the time-synchronized periodic wideband signals are transmitted by the two spaced apart base stations, wherein the beams face and overlap each other thereby defining the flight path for the unmanned aerial vehicle.

Embodiments of the present invention are described herein making reference to the appended drawings.

Equal or equivalent elements or elements with equal or equivalent functionality are denoted in the following description by equal or equivalent reference numerals.

In the following description, a plurality of details are set forth to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to one skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form rather than in detail in order to avoid obscuring embodiments of the present invention. In addition, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise.

<FIG> shows a schematic block diagram of an unmanned aerial vehicle (UAV) <NUM> according to an embodiment. The UAV <NUM> comprises a receiver <NUM> and a position determiner <NUM>. The receiver <NUM> is configured to receive two periodic wideband signals <NUM> and <NUM> transmitted from two spaced apart base stations of an UAV navigation system, wherein the two periodic wideband signals <NUM> and <NUM> are time-synchronized. The position determiner <NUM> is configured to determine a position of the UAV <NUM> relative to the two base stations based on a difference between reception times of the two periodic wideband signals <NUM> and <NUM> and/or based on reception intensities of the two periodic wideband signals <NUM> and <NUM>.

In detail, the receiver <NUM> can be configured to receive a first periodic wideband signal <NUM> from a first base station and a second periodic wideband signal <NUM> from a second base station. The first periodic wideband signal <NUM> and the second periodic wideband signal <NUM> can be time-synchronized, e.g., the first periodic wideband signal <NUM> and the second periodic wideband signal <NUM> can be transmitted at the same transmission time (or time instant). The position determiner <NUM> can be configured to determine a position of the UAV <NUM> relative to the first base station and the second base station based on a difference between a reception time of the first periodic wideband signal <NUM> and a reception time of the second periodic wideband signal <NUM>. Further or alternatively, the position determiner <NUM> can be configured to determine the position of the UAV <NUM> relative to the first base station and the second base station based on a reception intensity of the first periodic wideband signal <NUM> and a reception intensity of the second periodic wideband signal <NUM>.

<FIG> shows a schematic block diagram of a navigation system <NUM> for UAVs <NUM>, according to an embodiment. The navigation system <NUM> comprises two base stations <NUM> and <NUM> configured to transmit the two time-synchronized periodic wideband signals <NUM> and <NUM>, wherein the two base stations <NUM> and <NUM> are adapted to transmit the two periodic wideband signals <NUM> and <NUM> using beams <NUM> and <NUM> facing each other to create a flight path <NUM> for the UAV <NUM>.

In detail, the first base station <NUM> can be configured to transmit a first periodic wideband signal <NUM> using a first beam <NUM>, wherein the second base station <NUM> can be configured to transmit a second periodic wideband signal <NUM> using a second beam <NUM>. Thereby, the first beam <NUM> and the second beam <NUM> face and overlap each other to create a flight path <NUM> for the UAV <NUM>. The beams <NUM> and <NUM> may have beam widths of <NUM>° (or <NUM>°, or <NUM>°, or <NUM>° or <NUM>°) or less.

In other words, the first base station <NUM> can be configured to transmit the first periodic wideband signal <NUM> using a first beam <NUM> directed towards the second base station <NUM>, wherein the second base station <NUM> can be configured to transmit the second periodic wideband signal <NUM> using a second beam <NUM> directed towards the first base station, e.g., such that the first beam <NUM> and the second beam <NUM> overlap thereby defining a flight path <NUM> for the UAV <NUM>.

The two base stations <NUM> and <NUM> can be connected or in communication to each other in order to time synchronize the transmission of the two periodic wideband signals <NUM> and <NUM>. Further or alternatively, the navigation system <NUM> can comprise a central control system <NUM> configured to time synchronize the transmission of the two periodic wideband signals <NUM> and <NUM>, e.g., by controlling the base stations <NUM> and <NUM> to transmit the two periodic wideband signals <NUM> and <NUM> at the same transmission time (or time instant).

Subsequently, embodiments of both the UAV <NUM> and the UAV navigation system <NUM> are described in further detail.

The first periodic wideband signal <NUM> and the second periodic wideband signal <NUM> can be located in the extremely high frequency band (or millimeter band, e.g., <NUM> to <NUM>). The first periodic wideband signal <NUM> and the second periodic wideband signal <NUM> can have a bandwidth of <NUM> (<NUM> precision) to <NUM> (<NUM> precision). For example, the first periodic wideband signal <NUM> and the second periodic wideband signal <NUM> can be periodic wideband beacons, such as pulses and FMCW (FMCW = frequency modulated continuous wave radar).

The first periodic wideband signal <NUM> and the second periodic wideband signal <NUM> can be orthogonal to each other. For example, different frequency bands (f_a to f_b & f_b to f_c), spreading with orthogonal spreading codes (e.g. Gold code) or spatial multiplexing (directional antennas on UAV facing in different directions).

The receiver <NUM> of the UAV can be configured to use a window function (or window functions) for receiving the first periodic wideband signal <NUM> and the second periodic wideband signal <NUM>. For example, the receiver <NUM> can be configured to apply a window function (or window functions) to a receive signal in order to receive the first periodic wideband signal <NUM> and the second periodic wideband signal <NUM>. The window function may reduce multi-path propagation effects thereby increasing the accuracy of the position determination.

As already mentioned, the base stations <NUM> and <NUM> use facing beams <NUM> and <NUM> for transmitting the periodic wideband signals <NUM> and <NUM>, in order to define a flight path <NUM> for the UAV <NUM> that extends between the first base station <NUM> and the second base station <NUM>.

The UAV <NUM> can be configured to fly along the flight path <NUM> defined by the facing beams <NUM> and <NUM>.

The UAV navigation system <NUM> can be configured to transmit a control signal to the UAV <NUM>, the control signal comprising a flight direction assigning information assigning a flight direction to the UAV <NUM>. In that case, the UAV <NUM> can be configured to receive the control signal <NUM> and adapt its flight direction in dependence on the flight direction assigning information.

The UAV <NUM> can be configured to adapt its flight height in dependence on a flight direction. Further, the UAV navigation system <NUM> can be configured to transmit a control signal to the UAV <NUM>, the control signal comprising a flight height assigning information assigning a flight height to the UAV <NUM>. In that case, the UAV <NUM> can be configured to receive the control signal and adapt its flight height in dependence on the flight height assigning information. The UAV <NUM> can comprise, for example, a barometer in order to determine its flight height. Hereby it is possible to assign different flight heights to different UAVs, such that the same flight path <NUM> can be used by more than one UAV at the same time.

Note that the UAV <NUM> may not necessarily fly in the center of the flight path <NUM>, which may extend along the main or center beam directions of the two facing beams <NUM> and <NUM>. It is also possible that the UAV <NUM> is configured to fly offset to the center of the flight path (offset navigation), e.g., parallel to the center of the flight path <NUM> at a defined distance to the center of the flight path <NUM>. Thereby, the UAV <NUM> can be configured to adapt the distance to the center of the flight path in dependence on a flight direction or a control signal received from the UAV navigation system <NUM>, the control signal comprising a flight offset assigning information. Hereby it is possible that the same flight path <NUM> may be used by more than one UAV at the same time.

Further note that the flight path <NUM> for UAV may comprise at least two flight lanes, e.g., one or more flight lanes per flight direction, as will become clear from the following discussion of <FIG>, which shows a schematic top view of an UAV navigation system <NUM> and of an UAV <NUM>, according to an embodiment. As shown in <FIG>, the spaced apart flight lanes <NUM> and <NUM> may extend parallel to each other, e.g., in a horizontal direction and/or vertical direction. The UAV <NUM> can be configured to select one out of the least two flight lanes <NUM> and <NUM> based on a flight direction. Further, it is possible that the UAV navigation system <NUM> transmits a control signal comprising a flight lane assigning information assigning one of the two flight lanes <NUM> and <NUM> to the UAV <NUM>. In that case, the UAV <NUM> can be configured to select one out of the two flight lanes <NUM> and <NUM> based on the flight lane assigning information received from the UAV navigation system <NUM>. Hereby it is possible to assign different flight lanes to different UAVs, such that the same flight path <NUM> may be used by more than one UAV at the same time.

<FIG> shows a schematic top view of an UAV navigation system <NUM> and of an UAV <NUM>, according to an embodiment. In <FIG>, the two base stations <NUM> and <NUM> are configured to transmit four time-synchronized periodic wideband signals 106_1, 106_2, 108_1 and 108_2 using four beams 114_1, 114_2, 116_1 and 116_2, wherein two of the four beams of the two base stations face each other, respectively, to create two flight paths 118_1 and 118_2 between the two base stations <NUM> and <NUM>.

In detail, the first base station <NUM> can be configured to transmit a first periodic wideband signal 106_1 using a first beam 114_1 and a second periodic wideband signal 106_2 using a second beam 114_2. The second base station <NUM> can be configured to transmit a third periodic wideband signal 108_1 using a third beam 116_1 and a fourth periodic wideband signal 108_2 using a fourth beam 116_2. The first beam 114_1 and the third beam 116_1 face each other to define a first flight path 118_1 for the UAV <NUM>, wherein the second beam 114_2 and the fourth beam 116_2 face each other to define a second flight path 118_2 for the UAV <NUM>.

The UAV <NUM> can be configured to select one out of the two flight paths 118_1 and 118_2 between the two base stations <NUM> and <NUM> based on a flight direction. Further, the UAV navigation system <NUM> can be configured to transmit a control signal to the UAV <NUM>, the control signal comprising a flight path assigning information assigning one of the two flight path 118_1 and 118_2 to the UAV <NUM>. In that case, the UAV <NUM> can be configured to select one out of the two flight paths 118_1 and 118_2 between the two base stations <NUM> and <NUM> based on the flight path assigning information received from the UAV navigation system <NUM>.

Note that it is also possible that at least one of the flight paths 118_1 and 118_2 comprises at least two flight lanes, as discussed with reference to <FIG>, which may apply to one or both of the flight paths 118_1 and 118_2 of <FIG>.

<FIG> shows a schematic side view of an UAV navigation system <NUM> and of two UAVs 100_1 and 100_2. As already mentioned and described in detail above, the UAV navigation system <NUM> comprises two base stations <NUM> and <NUM> transmitting periodic wideband signals <NUM> and <NUM> using facing beams <NUM> and <NUM>. <FIG> shows in a diagram a time delay of a reception of the two periodic wideband signals <NUM> and <NUM> plotted over a position along the flight path <NUM> between the two base stations <NUM> and <NUM>. <FIG> shows in a diagram a received power of the two periodic wideband signals <NUM> and <NUM> plotted over a position along the flight path <NUM> between the two base stations <NUM> and <NUM>.

The basic structure of the proposed solution is a UAV positioning system <NUM> based on highly directive mm-wave beams <NUM> and <NUM> and a synchronized transmission of wideband pulses <NUM> and <NUM>. Equipped with a simple radio receiver module <NUM> (see <FIG>), the UAV <NUM> can be able to reliably determine its current location and also the designated flight direction. This solution is independent from the availability of a satellite positioning system and can therefore be used indoor or as a redundant system for areas with limited GNSS coverage, for instance in urban canyons near ground level.

Positioning can be accomplished with a synchronized transmission of wideband pulse <NUM> and <NUM> and the detection of these pulses <NUM> and <NUM> at the UAV <NUM>. The detected time difference between the pulses <NUM> and <NUM> allows the UAV <NUM> to estimate its position along the beams <NUM> and <NUM>. Apart from the time difference, the intensity of the pulses <NUM> and <NUM> can be used for estimation of the current position. Compared to using the signal strength only, the pulses make the positioning not vulnerable to multipath reflections, which are common in indoor environments. For instance, the use of a <NUM> pulse and a time windowing function enables the elimination of multipath components equivalent to <NUM> path length difference. This multipath suppression capability is sufficient for the envisioned application scenarios.

As shown in <FIG>, the proposed solution also allows for a two-way UAV traffic flow. This is accomplished by designating each flight direction a different airway height, hence a height offset between UAVs. The UAV may maintain its designated height by using barometer sensors, which are sufficiently accurate to accomplish this task.

For example, a first height may be assigned to a first flight direction (e.g., towards the first base station (mm-wave beacon node A) <NUM>) and a second height may be assigned to a second flight direction (e.g., towards the second base station (mm-wave beacon node B) <NUM>), such that a first UAV 100_1 flying in the first flight direction flies at the first flight height, wherein a second UAV 100_2 flying in the second flight direction flies at the second flight height.

<FIG> shows a schematic top view of an UAV navigation system <NUM> and of four UAVs 100_1 and 100_4. Similar to <FIG>, the two base stations <NUM> and <NUM> are configured to transmit four time-synchronized periodic wideband signals 106_1, 106_2, 108_1 and 108_2 using four beams 114_1, 114_2, 116_1 and 116_2, wherein two of the four beams of the two base stations face each other, respectively, to create two flight paths between the two base stations <NUM> and <NUM>. In addition to <FIG>, in <FIG> it indicated that different flight heights can be assigned to different flight directions within each flight path. This is also indicated in further detail in <FIG>, which shows a cross-sectional view of the two flight paths going from the second base station <NUM> to the first base station (mm-wave beacon node A) <NUM>.

For example, a first flight height can be assigned to the third and fourth UAVs 100_3 and 100_4 flying in a first direction (e.g., towards the first base station (mm-wave beacon node A) <NUM>), wherein a second flight height can be assigned to the first and second UAVs 100_1 and 100_2 flying in a second direction (e.g., towards the second base station (mm-wave beacon node B) <NUM>).

<FIG> shows a schematic top view of an UAV navigation system <NUM>, according to an embodiment. As shown in <FIG>, the navigation system can further comprise a relay base station <NUM> arranged in the flight path <NUM> between the two base stations <NUM> and <NUM> and configured to retransmit the periodic wideband signals <NUM><NUM> received from the two base stations <NUM> and <NUM> to the respective other base station of the two base stations <NUM> and <NUM> using two beams facing the respective beams of the two base stations <NUM> and <NUM>.

In detail, the relay base station <NUM> can be configured to receive the first periodic wideband signal <NUM> from the first base station <NUM> and to retransmit the first periodic wideband signal <NUM>' to the second base station <NUM> using a third beam <NUM>' facing the second beam <NUM> of the second base station <NUM>. Further, the relay base station <NUM> can be configured to receive the second periodic wideband signal <NUM> from the second base station <NUM> and to retransmit the second periodic wideband signal <NUM>' to the first base station using a fourth beam <NUM>' facing the first beam <NUM> of the first base station <NUM>.

<FIG> shows a schematic top view of an UAV navigation system <NUM>, according to an embodiment. As shown in <FIG>, the navigation system <NUM> can comprise two further base stations <NUM> and <NUM> configured to transmit two further time-synchronized periodic wideband signals <NUM> and <NUM> using further beams <NUM> and <NUM> facing each other to create a further flight path <NUM>, wherein the flight path <NUM> and the further flight path <NUM> cross each other (intersection).

<FIG> shows an application example of the UAV navigation system <NUM> in which the base stations <NUM> and <NUM> are integrated in street lamp <NUM> and <NUM>. In other words, <FIG> shows a possible application example, where the mm-wave beacon nodes <NUM> and <NUM> are installed on two lamp posts and UAV <NUM> flies along the defined airway.

Embodiments provide the following benefits. First, automated and safe navigation of UAVs with limited (in street canyons) or no (indoor) GNSS coverage. Second, mm-wave beam infrastructure reduces the costs per UAV, since costly sensors and computationally costly data processing become obsolete. Third, mm-wave beam infrastructure can be used as both: as a navigation system and as a high data rate communication system. Fourth, secure against attacks on GNSS signal: "GNSS spoofing" [<NPL>] - as it doesn't use GNSS. Fifth, securing obstacle-free airways can easily be accomplished, since obstruction of the line-of-sight beam is directly detected by the system. Navigation along LOS beam has by definition no obstacle. Flyable paths are inherently without obstacles (buildings etc.), which makes path planning simpler. One advantage of such a system based on defined UAV "air ways" is the fact that the search for "flyable paths in 3D" without any obstacles, as stated in [<NPL>] is not further needed.

Embodiments may be applied in several fields. For example, future UAV systems, for instance used for delivery services, usually fly along predefined paths in order to reach their assigned destination. Similar to airplanes, the installation of so-called airways guarantees that the UAV stays on the designated route.

The proposed solution permits the installation of an UAV navigation network. Such a system enables "a large number of relatively low-cost UAVs to fly beyond-line-of-sight without costly sensing and communication systems or substantial human intervention in individual UAV control. Under current free-flight-like paradigm, wherein a UAV can travel along any route as long as it avoids restricted airspace and altitudes. However, this requires expensive on-board sensing and communication as well as substantial human effort in order to ensure avoidance of obstacles and collisions. The increased cost serves as an impediment to the emergence and development of broader UAV applications. Available GPS-based navigation can be used to fly the UAV along the selected route and time schedule with relatively low added cost, which therefore, reduces the barrier to entry into new UAV-applications market.

<FIG> shows a flowchart of a method <NUM>, according to an embodiment. The method <NUM> comprises a step <NUM> of receiving two periodic wideband signals transmitted from two spaced apart positions, wherein the two periodic wideband signals are time-synchronized. Further, the method <NUM> comprises a step <NUM> of determining a position of the unmanned aerial vehicle relative to the two spaced apart positions based on a difference between reception times of the two periodic wideband signals and based on reception intensities of the two periodic wideband signals.

<FIG> shows a flowchart of a method <NUM>, according to an embodiment. The method <NUM> comprises a step <NUM> of transmitting two time-synchronized periodic wideband signals from two spaced apart positions using beams facing each other to create a flight path for an unmanned aerial vehicle.

<FIG> shows a flowchart of a method <NUM>, according to an embodiment. The method <NUM> comprises a step <NUM> of transmitting two time-synchronized periodic wideband signals from spaced apart positions using beams facing each other to create a flight path for an UAV. Further, the method <NUM> comprises a step <NUM> of receiving the two periodic wideband signals at the UAV. Further, the method comprises a step <NUM> of determining a position of the unmanned aerial vehicle relative to the two spaced apart positions based on a difference between reception times of the two periodic wideband signals and based on reception intensities of the two periodic wideband signals.

In embodiments, the UAV navigation system <NUM> comprises two mm-wave beacon nodes <NUM> and <NUM> transmitting synchronized orthogonal beacons <NUM> and <NUM> using narrow beams facing each other to create a flight path for the UAV <NUM>. Thereby, positioning of the UAV is accomplished by detecting an intensity and time difference of the beacons <NUM> and <NUM>. Further, a position-based navigation and control of the UAV <NUM> may be performed. Some embodiments provide multi-path suppression. For that purpose, orthogonal wideband beacons (pulse, FMCW, etc.) can be transmitted. Further or alternatively, a time windowing can be used to reduce multi-path effects.

Some embodiments provide offset navigation. Offset flight can be used to enable multiple UAVs on a single flight path by avoiding blocking.

Some embodiments provide an extension to two beams per node (or base station). Two beams per node can be introduced to enable two-way UAV flights. Further, it is possible to use barometer sensors, for example, in order to demine the flight height of the UAV and to adapt the flight height in dependence on a flight direction.

Some embodiments provide an extension to four beams per node. Thereby, four lanes per path can be created. Further, an adaptive direction control (signaling) of lanes can be used.

Some embodiments provide a flight path relay. Thereby, a relay node with two mm-wave beacons with different direction can be used. Further, offset navigation can be used to avoid collision with relay node.

Some embodiments provide an intersection. Thereby, a relay node with four mm-wave beacons can be used to create intersection of two flight paths. Further, offset navigation can be used to avoid crush with intersection node. Further, a transfer to different flight path can be used.

Some embodiments provide a central control system. A central control server and wireless control network can be introduced, for example, to collect positions of all UAVs in a field and control them simultaneously.

Some of the method steps may be executed by (or using) a hardware apparatus, like for example, a microprocessor, a programmable computer or an electronic circuit. Some other of the method steps, such as transmitting or receiving wideband signals, cannot be executed using generic data processing means. The following embodiments thus refer only to the method steps that can be executed by generic data processing means.

Claim 1:
Unmanned aerial vehicle (<NUM>), comprising:
a receiver (<NUM>) configured to receive two periodic wideband signals (<NUM>,<NUM>) transmitted from two spaced apart base stations (<NUM>,<NUM>) of a navigation system (<NUM>) for unmanned aerial vehicles, wherein the two periodic wideband signals (<NUM>,<NUM>) are time-synchronized; and
a position determiner (<NUM>) configured to determine a position of the unmanned aerial vehicle (<NUM>) relative to the two base stations (<NUM>,<NUM>) based on a difference between reception times of the two periodic wideband signals (<NUM>,<NUM>) and based on reception intensities of the two periodic wideband signals (<NUM>,<NUM>);
wherein the unmanned aerial vehicle (<NUM>) is configured to fly along a flight path (<NUM>) defined by beams (<NUM>,<NUM>) using which the two wideband signals (<NUM>,<NUM>) are transmitted by the two base stations (<NUM>,<NUM>);
characterized in that
the beams (<NUM>,<NUM>) face and overlap each other thereby defining the flight path (<NUM>) for the unmanned aerial vehicle (<NUM>).