Reduction of interference caused by aerial vehicles

Abstract

The present invention provides a method of reducing interference caused by an aerial vehicle in a mobile communications system, the method comprising arranging for the aerial vehicle to steer radio transmissions when the aerial vehicle is airborne such that a direction of the transmissions is adjusted to be directed vertically downward.

Claims

1. A method of reducing interference caused by an aerial vehicle in a mobile communications system, the method comprising: arranging for the aerial vehicle to steer radio transmissions when the aerial vehicle is airborne to compensate for a tilt of the aerial vehicle such that a direction of the radio transmissions is adjusted to be directed vertically downward and wherein the aerial vehicle adapts a beam width of the radio transmissions such that a footprint of the beam on the ground is controlled in relation to a determined cell size of a base station communicating with the aerial vehicle, the determined cell size of the base station being determined by the aerial vehicle from a reference signal power value parameter broadcast by the base station.

2. The method according to claim 1, wherein the beam width is adapted using a measure of an altitude of the aerial vehicle above ground and a function of the determined cell size.

3. The method according to claim 1, wherein the aerial vehicle controls a beam width of the radio transmissions such that a footprint of the beam on the ground is controlled in relation to an estimated transmission range of user equipment operating at ground level.

4. The method according to claim 3, wherein a received maximum transmit power parameter is used to determine a value for the estimated transmission range.

5. The method according to claim 1, wherein the aerial vehicle controls a beam width of the radio transmissions such that a footprint of the beam on the ground is controlled in relation to a predetermined value.

6. The method according to claim 1, wherein the aerial vehicle controls a beam width of the radio transmissions such that a footprint of the beam on the ground is controlled in relation to a received signal power from a selected base station of the mobile communications system.

7. The method according to claim 6, wherein the aerial vehicle performs measurements of received signal power from the selected base station with a varying selected receive beam width until the received signal power is below a predetermined threshold and a value of a receive beam width generating the received signal power below the predetermined threshold is used as the beam width for the radio transmissions from the aerial vehicle.

8. The method according to claim 1, wherein a measure of an altitude of the aerial vehicle above the ground is used to control the beam width.

9. The method according to claim 1, wherein a measurement of aerial vehicle flight attitude is used to control a steering of the direction of the radio transmissions.

10. The method according to claim 1, wherein the radio transmissions are steered once the aerial vehicle exceeds a predetermined height above the ground.

11. An aerial vehicle including a user equipment module adapted to perform the method of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawing in which

(2) FIG. 1 illustrates a situation where a drone can cause interference in a neighbouring cell;

(3) FIG. 2 illustrates a situation where a drone can cause sidelink interference for UEs operating in a neighbouring cell;

(4) FIG. 3 illustrates varying a beam width with height;

(5) FIG. 4 illustrates controlling a drone footprint in accordance with a cell range;

(6) FIG. 5 illustrates controlling a drone footprint in accordance with a maximum transmission range;

(7) FIG. 6 illustrates varying a beam width according to a received signal power parameter;

(8) FIG. 7 illustrates steps performed according to a method of the invention; and

(9) FIG. 8 illustrates varying a beam direction with drone attitude.

DETAILED DESCRIPTION

(10) In a first embodiment, a footprint range (FPR) is calculated by using an indication of the transmit range (=cell radius) of the serving cell as illustrated by FIG. 4. The beam width is then adjusted based on the drone's altitude to deliver a footprint range almost equal to the cell radius. E.g. in LTE, the cell radius could be estimated from the “reference signal power” (P.sub.Ref). This parameter is the transmit power of the cell-specific downlink reference signals. It is broadcast by each cell in system information block (SIB) type 2 and the value range is from −60 dBm to +50 dBm. Equation (1) could be used to calculate the FPR value. It considers path loss calculations from a pathloss model such as that described at www.wirelesscommunication.nl/reference/chaptr03/pel/loss.htm:

(11) $\begin{array}{cc}\mathrm{FPR}=\frac{1}{\sqrt{D_0*f_c}}*{10}^{\frac{P_{\mathrm{ref}}-24\mathrm{dBm}+B_{\mathrm{DL}}}{40}}*C_{\mathrm{DL}}& \left(1\right)\end{array}$

(12) where

(13) FPR is the footprint range covered by the transmit beam of the drone-UE

(14) D.sub.0 is a constant factor of 748 [1/m.sup.2*MHz]

(15) P.sub.ref is the reference signal power as broadcast by the eNB

(16) f.sub.c is the downlink carrier frequency in MHz as indicated by the eNB

(17) B.sub.DL is the downlink link budget for a transmit power of 24 dBm calculated according to a method described in an online LTE encyclopaedia at https://sites.google.com/site/lteencyclopedia/lte-radio-link-budgeting-and-rf-planning. Typically, not all required parameters for calculation of the link budget are known by the UE. In this case, the missing parameters are assumed to be the same as used in the example in the LTE encyclopaedia. If no parameter is known or if a rough estimation for the sake of simplicity is considered to be sufficient, the value 165.5 dBm could be used for B.sub.DL (c.f. Table 1)

(18) C.sub.DL is a constant factor in the range of [0.1 to 10] used to adapt the FPR in relation to the cell range. The value “1” means, that the FPR equals the cell range. The value is either preconfigured in the UE or signalled by the mobile network to the UE.

(19) In a second embodiment, the footprint range (FPR) of the drone is calculated to be smaller or equal to the maximum transmit range of zero-altitude UEs as illustrated by FIG. 5. The maximum transmit range of zero-altitude UEs for a given serving cell could be estimated e.g. in LTE from the parameter “P.sub.MAX”. This is the cell-specific maximum UE transmit power. It is broadcast by each cell in SIB1. Equation (2) could be used to calculate the FPR value. It considers path loss calculations from a path loss model such as that described at www.wirelesscommunication.nl/reference/chaptr03/pel/loss.htm.

(20) $\begin{array}{cc}\mathrm{FPR}=\frac{1}{\sqrt{D_0*f_c}}*{10}^{\frac{P_{\mathrm{MAX}}-24\mathrm{dBm}+B_{\mathrm{UL}}}{40}}*C_{\mathrm{UL}}& \left(2\right)\end{array}$

(21) where

(22) FPR is the footprint range covered by the transmit beam of the drone-UE

(23) D.sub.0 is a constant factor of 748 [1/m.sup.2*MHz]

(24) P.sub.MAX is the maximum UE transmit power as broadcast by the eNB

(25) f.sub.c is the Uplink carrier frequency in MHz as indicated by the eNB

(26) B.sub.UL is the Uplink link budget for a transmit power of 24 dBm calculated in a manner described in the LTE encyclopaedia referred to above. Typically, not all required parameters for calculation of the link budget are known by the UE. In this case, the missing parameters are assumed to be the same as used in the example in the LTE encyclopaedia. If no parameter is known or if a rough estimation for the sake of simplicity is considered to be sufficient, the value 149.5 dBm could be used for B.sub.UL. (c.f. Table 2. Instead of 64 kbps data rate 1 Mbps is used to obtain similar conditions as assumed for the downlink).

(27) C.sub.UL is a constant factor in the range of [0.1 to 10] used to adapt the FPR in relation to the maximum transmit range of zero-altitude UEs. The value “1” means, that the FPR equals the transmit range of zero-altitude UEs. The value is either preconfigured in the UE or signalled by the mobile network to the UE.

(28) In the first and second embodiments, the FPR is calculated individually for each cell. In a third embodiment, the FPR is a semi-static value, which is pre-known by the drone-UE and which may optionally be configurable by the network. The beam width (BW) could be calculated according to equation (3). The principle is depicted in FIG. 3.

(29) $\begin{array}{cc}\mathrm{BW}=2*\arctan \left(\frac{FPR}{\mathrm{Alt}}\right)& \left(3\right)\end{array}$

(30) It is typical for embodiments one to three, that only a slow adaption rate for the beam width of the adaptive antenna system is required, e.g. if the drone holds a certain altitude, only one beam width adaption after a handover to another cell may be required, if the new cell uses a different cell radius. Alternatively, no adaption is required until the drone left a certain altitude corridor. This is for the case where no cell-specific beam width adaption is used, or where the cell radius is the same for the new cell. The method is therefore best suited for drones that typically fly at certain altitudes, like delivery drones but also for all other kind of drones. The costs (e.g. battery consumption and processor resources) for the method are very low.

(31) In a fourth embodiment, the beam width of the UE-Tx-beam is adjusted according to the received signal power from the serving or from neighbouring cells. Therefore, the drone-UE performs measurements of the received signal power from the selected base station. In case of an LTE base station (eNB), the RSRP value could be used (cf. 3GPP TS 36.214). In case that a neighbouring cell should be used, it selects the best neighbouring cell (e.g. the cell with the highest reference signal received power (RSRP)). For this measurement, the drone-UE uses a wide UE-Rx-beam width, that ensures that the measured cell is within this beam. Then the drone-UE repeats the measurement at the selected cell with reduced beam width. It makes further measurements with further reduced beam width, until the measured RSRP is about a certain offset smaller (e.g. 3 dB) compared to the initial measurement (which applies the wide beam). The UE-Rx-beam width of the latest measurement is than used for the UE-Tx-beam of the drone-UE provided the reception of the serving base station does not suffer (this can be ensured by performing these measurements very fast, e.g. within a few seconds). It will periodically proceed with the RSRP measurement and will adapt the beam width accordingly. In case that neighbour cell measurements are required, they will be performed by using a wide beam. Additionally, a fixed or configurable ratio R (e.g., in the range between 0.6 and 1.0) between the widths of UE-Tx-beam and UE-Rx-beam could be defined, for instance according to the formula (4).

(32) $\begin{array}{cc}R=\frac{{\mathrm{BW}}_{\mathrm{UE}\text{-}\mathrm{Tx}\text{-}\mathrm{Beam}}}{{\mathrm{BW}}_{\mathrm{UE}\text{-}\mathrm{Rx}\text{-}\mathrm{Beam}}}=0.8& \left(4\right)\end{array}$

(33) In a fifth embodiment, the beam width is controlled and adjusted as described in the foregoing embodiments. In addition, the beam is not directed vertically to the ground but it is directed towards the base station. This ensures the maximum beam antenna gain is used in communication with the base station which may reduce the necessary transmit power and thus decrease interference on other cells. The angle of deflection may be estimated from a measured angle of arrival or from geo location estimations of the UE relative to the base station.

(34) In one embodiment of the present invention the drone is equipped with means to autonomously keep the beam orientation during various flight manoeuvres vertically to the ground thereby compensating for tilt movements the drone might undergo in moments of acceleration or deceleration, or lateral movements in general. This function which we term a “plumb line” function used to derive the beam direction may be realized by means of inertial sensors, gyroscopes, magnetometers, or other types of sensors, so that the drones is enabled to keep an angle α between an orientation of the antenna system and the downward virtual plumb line as small as possible as illustrated by FIG. 8.

(35) It is to be noted that the beam width described above is related to the antennas used for transmission, i.e. a UE-Tx-beam is generated. In most cases the same antenna characteristic can also be used for reception, i.e. the calculated parameters could be re-used to configure the antennas used in the receiver of the UE (UE-Rx-beam). This may be not useful in cases, where different base stations at different locations are used for uplink and downlink and in some cases, if the frequency offset between downlink and uplink is very large. Further, downlink measurements may lead to unexpected results, if a directed antenna characteristic is used. Therefore, an omni-polar characteristic is preferred for measurement purposes.

(36) In the following example, it is assumed, that an LTE-based mobile network is serving the drone-UE. Nevertheless, the principles of the invention are also applicable if another type of mobile communication system is used, e.g. GSM, UMTS or any new type like 5G.

(37) A drone is equipped with a UE, whereas the antennas are designed to send a directed beam downwards to the ground. The beam width is configurable between 10 and 180 degree and “omni-directional”.

(38) A procedure to configure the beam width described below. The drone's flight track for this example is depicted in FIG. 7. The circled numbers in the figures corresponds to the numbering of the steps below.

(39) 1. The drone (incl. the drone-UE) is switched on. The drone-UE connects to the mobile network via eNB A. It obtains the reference signal power P.sub.Ref from eNB A and uses a omni-directional antenna characteristic for transmission and reception.

(40) 2. The drone lifts off. It starts monitoring the altitude (e.g. by using a sonar sensor). It was previously configured with an altitude threshold Alt.sub.min (either previously stored in the UE or, configured by the network). In this example Alt.sub.min, cell_A=20 m was signalled by the eNB A to the drone-UE. That means, in this example, each cell may choose to configure the drone-UE with a different value for the Alt.sub.min parameter. The drone-UE will use omni-directional antenna characteristic until this threshold is exceeded.

(41) 3. The drone further gains height. After detection that Alt.sub.min was exceeded, it starts to use the beam width control function, i.e. it calculates the value for FPR according to formula (1), which is valid for the current serving cell, i.e. no new calculation will be required until the next hand over. Further it calculates the beam width “BW .sub.cell A” with the current altitude and the FPR according to equation (3). This is done either periodically (e.g. once per second) or event driven if the difference of the current altitude to the altitude used for the previous calculation exceeds a certain value. The latter is most efficient if the drone holds a certain altitude.

(42) 4. During the flight, the drone-UE performs neighbour cell measurements as usual for a UE. Such measurements will be performed by using the omni-directional antenna characteristic.

(43) 5. At some point in time, these measurements indicate the need for a handover to cell B. Therefore, the drone-UE performs the handover to cell B as usual. And in addition, the drone-UE derives the values P.sub.Ref and Alt.sub.min,cell_B from eNB B.

(44) 6. The drone-UE applies the newly received parameter P.sub.Ref to calculate FPR and the beam width “BW .sub.cell B”. In the example in FIG. 7, P.sub.Ref of cell B and therefore the cell range is much larger than P.sub.Ref of cell A. Therefore, the FPR will be much larger after the handover.

(45) 7. The drone comes closer to the landing area and starts to decrease altitude.

(46) 8. The drone-UE detects, that the current altitude falls below Alt.sub.min,cell_B. Therefore, it stops using the beam width control function. It will use now an omni-directional antenna characteristic

(47) 9. The drone has landed and is switched off.

(48) TABLE-US-00001 TABLE 1 Data rate (Mbps) 1 Transmitter - eNode B a HS-DSCH power (dBm) 46.0  b TX antenna gain (dBi) 18.0  c Cable loss (dB) 2.0 d EIRP (dBm) 62.0 = a + b + c Receiver - UE e UE noise figure (dB) 7.0 f Thermal noise (dBm) −104.5 = k(Boltzmann) * T(290K) * B(360 kHz) g Receiver noise floor (dBm) −97.5 = e + f h SINR (dB) −10.0 From Simulations performed i Receiver sensitivity (dBm) −107.5 = g + h j Interference Margin (dB) 3.0 k Control Channel 1.0 Overhead (dB) l RX antenna gain (dBi) 0.0 m Body Loss (dB) 0.0 Maximum path loss 165.5 = d − i − j − k + l − m

(49) Downlink link budget (=“Maximum path loss”) for 1 Mbps with dual-antenna receiver terminal (from “LTE encyclopaedia”).

(50) TABLE-US-00002 TABLE 2 Data rate (kbps) 64 Transmitter - UE a Max. TX power (dBm) 24.0  b TX antenna gain (dBi) 0.0 c Body loss (dB) 0.0 d EIRP (dBm) 24.0 = a + b + c Receiver - eNode B e Node B noise figure (dB) 2.0 f Thermal noise (dBm) −118.4 = k(Boltzmann) * T(290K) * B(360 kHz) g Receiver noise floor (dBm) −116.4 = e + f h SINR (dB) −7.0 From Simulations performed i Receiver sensitivity (dBm) −123.4 = g + h j Interference Margin (dB) 2.0 k Cable Loss (dB) 2.0 l RX antenna gain (dBi) 18.0  m MHA gain (dB) 2.0 Maximum path loss 163.4 = d − i − j − k + l − m

(51) Uplink link budget (=“Maximum path loss”) for 64 kbps with dual-antenna receiver base station (from “LTE encyclopaedia”).