Transmission of synchronization signals

There is provided mechanisms for transmission of synchronization signals. A method is performed by a network node. The method comprises transmitting polarized bursts of SSB in beams. One SSB is transmitted per each beam in each burst. Polarization of at least one of the SSBs changes between two consecutive bursts of the SSBs.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a 35 U.S.C. § 371 National Stage of International Patent Application No. PCT/EP2019/057539, filed Mar. 26, 2019, designating the United States.

TECHNICAL FIELD

Embodiments presented herein relate to a method, a network node, a computer program, and a computer program product for transmission of synchronization signals.

BACKGROUND

Synchronization Signal Block (SSB) is a signal that is broadcast over the New Radio (NR) air interface from network nodes on the network side to terminal devices on the user side. The SSB is intended to enable initial synchronization of the terminal devices, provide basic system information to the terminal devices as used for initial access, and allow the terminal device to perform mobility measurements. The structure of an SSB is illustrated inFIG.1. In particular,FIG.1schematically illustrates time/frequency resources for transmitting one the SSB (where PRB is short for Physical resource Block). Each SSB consist of four orthogonal frequency-division multiplexing (OFDM) symbols, inFIG.1denoted OFDM symb1, OFDM symb2, OFDM symb3, and OFDM symb4. Time/frequency resources for an NR Primary Synchronization Signal (PSS) are located in the first OFDM symbol and are used for finding a coarse time/frequency synchronization. Time/frequency resources for an NR Physical Broadcast Channel (PBCH) are located in the second, third and fourth OFDM symbol and contain necessary system information bits. Time/frequency resources for an NR Secondary Synchronization Signal (SSS) are located in the third OFDM symbol and are used for establishing a finer time/frequency synchronization.

The PSS and SSS of the SSB are transmitted over 127 subcarriers, where the subcarrier spacing could be 15 kHz or 30 kHz for carrier frequencies below 6 GHz, and 120 kHz or 240 kHz for carrier frequencies above 6 GHz. For low carrier frequencies (such as carrier frequencies below 6 GHz), each network node might transmit one cell-wide SSB that thus covers the whole cell served by the network node, whilst for higher carrier frequencies (such as carrier frequencies above 6 GHz) each network node might transmit several beamformed SSBs to attain coverage over the whole cell. In some examples the maximum number of SSB per cell are 4 for carrier frequencies below 3 GHz, 8 for carrier frequencies in the interval 3-6 GHz, and 64 for carrier frequencies above 6 GHz. The SSBs might be transmitted in an SSB burst which could last up to 5 ms. The periodicity of the SSB burst might be configurable. In some examples the periodicity is 5, 10, 20, 40, 80, or 160 ms.

As mentioned above, terminal devices could use SSBs for mobility (i.e. cell selection) purposes. The terminal device might then perform measurements of reference signal received power (RSRP) on the SSS of the SSB. However, it could be difficult for the terminal devices to obtain accurate RSRP values when measuring on the SSS.

Hence, there is still a need for an improved cell selection procedure.

SUMMARY

An object of embodiments herein is to provide efficient transmission of synchronization signals enabling efficient cell selection.

According to a first aspect there is presented a method for transmission of synchronization signals. The method is performed by a network node. The method comprises transmitting polarized bursts of SSB in beams. One SSB is transmitted per each beam in each burst. Polarization of at least one of the SSBs changes between two consecutive bursts of the SSBs.

According to a second aspect there is presented a network node for transmission of synchronization signals. The network node comprises processing circuitry. The processing circuitry is configured to cause the network node to transmit polarized bursts of SSB in beams. One SSB is transmitted per each beam in each burst. Polarization of at least one of the SSBs changes between two consecutive bursts of the SSBs.

According to a third aspect there is presented a network node for transmission of synchronization signals. The network node comprises a transmit module configured to transmit polarized bursts of SSB in beams. One SSB is transmitted per each beam in each burst. Polarization of at least one of the SSBs changes between two consecutive bursts of the SSBs.

According to a fourth aspect there is presented a computer program for transmission of synchronization signals, the computer program comprising computer program code which, when run on a network node, causes the network node to perform a method according to the first aspect.

According to a fifth aspect there is presented a computer program product comprising a computer program according to the fourth aspect and a computer readable storage medium on which the computer program is stored. The computer readable storage medium could be a non-transitory computer readable storage medium.

Advantageously this transmission of synchronization signals enables efficient cell selection for terminal devices receiving the synchronization signals.

Advantageously this reduces the risk of polarization mismatching. In turn, this reduces the risk of erroneous cell-selection. Also the risk of unwanted handovers due to, for example, rotation of the terminal device are reduced, which otherwise would cause unnecessary overhead signaling.

Advantageously this is achieved with low implementation effort, complexity, and processing need.

DETAILED DESCRIPTION

FIG.2is a schematic diagram illustrating a communications network100awhere embodiments presented herein can be applied. The communications network100could be a third generation (3G) telecommunications network, a fourth generation (4G) telecommunications network, or a fifth (5G) telecommunications network and support any 3GPP telecommunications standard, where applicable.

The communications network100comprises a network node200configured to provide network access to at least one terminal device150in a radio access network110. The radio access network110is operatively connected to a core network120. The core network120is in turn operatively connected to a service network130, such as the Internet. The terminal device150is thereby enabled to, via the network node200, access services of, and exchange data with, the service network130.

The network node200comprises, is collocated with, is integrated with, or is in operational communications with, a transmission and reception point (TRP)140. The network node200(via its TRP140) and the terminal device150are configured to communicate with each other in respective sets of beams160,170, where, as illustrated inFIG.2, the set of beams160consists of N individual beams160a,160b, . . . ,160N, and the set of beams170at least comprises individual beams170a,170b.

Examples of network nodes200are radio access network nodes, radio base stations, base transceiver stations, Node Bs, evolved Node Bs, g Node Bs, access points, and access nodes, and backhaul nodes. Examples of terminal devices150are wireless devices, mobile stations, mobile phones, handsets, wireless local loop phones, user equipment (UE), smartphones, laptop computers, tablet computers, network equipped sensors, network equipped vehicles, and so-called Internet of Things devices.

As disclosed above there is a need for an improved cell selection procedure. In further detail, as mentioned above, terminal devices150could use SSBs for mobility (i.e. cell selection) purposes using measurements of RSRP. The terminal device150might filter the measurements of RSRP as obtained from SSBs received from one or more network nodes200using layer 3 filtering (as specified in Section 5.5.3.2 of 3GPP TS 38.331 “NR; Radio Resource Control (RRC); Protocol specification”, Release 15, version 15.4.0, dated 14 Jan. 2019) according to the following:
Fi=(1−a)·Fi+1+a·MiEquation 1

In Equation 1, Miis the current received measurement of RSRP (i.e., the measurement of RSRP at time index i), Fiis the updated filtered measurement result (i.e., the filtered measurement result at time index i), and Fi−1is the most previous filtered measurement result (i.e., the filtered measurement result at time index i−1). The parameter “a” defines how much of the current measurement should be weighted compared to previous measurements. The parameter “a” therefore typically takes a value between 0 and 1. With a reasonable parameter setting of “a” the mobility measurement used for cell-selection is filtered over time to remove fast fading effects that possibly could cause ping-pong effects (i.e. unwanted handovers that “moves” one terminal device150back and forth between two (or more) serving network node S200).

The reporting of the mobility measurements from the terminal device150to the network node200can be either periodic or event based. For periodic reporting the network node200configures the terminal device150to report the mobility measurements periodically for all neighbouring cells detected on the associated frequency where the terminal device150reports up to “maxCellReport” number of cells. For event triggered report the terminal device150is configured to report mobility measurements for all cells defined by the parameter “triggeredCellsList”, again up to “maxCellReport” number of cells. The even trigger report is signalled from the terminal device150when a number of criteria are met, as described in Section 5.5.4 of aforementioned document 3GPP TS 38.331. In case the network node200detects (through a mobility report from the terminal device150) that a neighbouring cell is stronger than serving cell it can initiate a handover process for the terminal device150. A handover process generally requires quite much signalling and overhead and unnecessary handovers should be avoided as much as possible.

Since the SSS only covers127subcarriers and that the subcarrier spacing for carrier frequencies below 6 GHz could be either 15 kHz or 30 kHz, the total bandwidth for the SSS becomes rather small (around 2 MHz-4 MHz) and might hence be rather sensitive to frequency selective behavior in the radio propagation channel between the TRP140and the terminal device150(for example down fading of certain polarizations over a certain frequency band etc.). In addition, the SSB is only transmitted on a single port (i.e. with a single polarization), which means that polarization mismatch might occur between the network node200and the terminal device200. This might lead to terminal devices establishing, or at least seeking to establishing, a connection to the erroneous network node200.

Due to the physical geometry of the terminal device150the currents of the antennas might be limited in certain directions which means that the antenna gain for the polarization in those directions become very small. As an illustrative example, if a common terminal device150, which generally has the physical geometry of a relatively flat cuboid, is held in a horizontal position, the antenna gain will be smaller, or even much smaller, for the vertical polarization than for the horizontal polarization (in all directions). Then, in case the network node200transmits an SSB with vertical polarization, the terminal device150will have very low RSRP for that SSB, unless the radio propagation channel shifts the polarization state of the transmitted signal. At mmWave frequencies, however, the cells are assumed to be rather small due to poor propagation properties and it is therefore expected that the line of sight (LOS) probability to terminal device150is rather high. For LOS conditions the polarization state is to large extent expected to be maintained in the radio propagation channel between the TRP140and the terminal device150.

Further, different polarizations might have very different measured RSRP. For example, the beam for which strongest RSRP can be measured in one polarization might be the weakest when measuring the RSRP in the orthogonal polarization. This means that depending on which polarization is used for the SSB, the terminal device150might experience different levels of RSRP. This in turn might result in that the terminal device150will be connected to different cells depending on for which polarization the RSRP of the SSB is measured. Further, if the terminal device150is rotated, or pivoted, such that it changes the polarization state of its receive antenna patterns, an unwanted and unnecessary handover might be initiated.

FIG.3is a schematic diagram illustrating a communications network100bcomprising two sites180a,180b, where each site180a,180bcomprises a network node200and TRP140as disclosed above with reference toFIG.2. A terminal device150is located in between the sites180a,180bat a distance D1 from the TRP140of site180aand at a distance D2 from the TRP140of site180b. It is in this example assumed that D1<D2 which would indicate that the path gain is higher to the TRP140of site180athan to the TRP140of site180b. In the illustrative example ofFIG.3it is assumed that SSBs of polarization P1 is transmitted from both sites. In the illustrative example ofFIG.3P1 is further assumed to define vertical polarization, and P2 is assumed to define horizontal polarization. The terminal device150is further assumed to be placed in a horizontal position, which typically means that the antenna gain, as illustrated by beam170b, for the vertical polarization (i.e., P1) is lower than for the horizontal polarization (i.e., P2), as illustrated by beam170a. In this respect, the radiation pattern and polarization state is typically quite random at the terminal device15o, and in this case the radiation pattern implies that beams170a,170bfor vertical and horizontal polarization are pointing in opposite directions. Since the beam170bfor the vertical polarization is pointing in direction towards site180ba connection, as resulting from the aforementioned mobility measurements, will be established between the terminal device150and the network node200of site180b. However, it would have been better if instead a connection would have been established between the terminal device150and the network node200of site180a, although for the aforementioned reasons this will not be the case.

The embodiments disclosed herein therefore relate to mechanisms for transmission of synchronization signals. In order to obtain such mechanisms there is provided a network node200, a method performed by the network node200, a computer program product comprising code, for example in the form of a computer program, that when run on a network node200, causes the network node200to perform the method.

FIG.4is a flowchart illustrating an embodiment of a method for transmission of synchronization signals. The methods are performed by the network node200. The methods are advantageously provided as computer programs920.

The network node transmits the SSBs using different polarizations P1, P2. In particular, the network node200is configured to perform step S102:

S102: The network node200transmits polarized bursts of SSBs in beams160. One SSB is transmitted per each beam160a:160N in each burst. The polarization P1, P2 of at least one of the SSBs (i.e., the polarization according to which the at least one of the SSBs is transmitted) changes between two consecutive bursts of the SSBs.

Thereby, instead of the serving cell for the terminal device150being selected based on strongest RSRP for SSBs transmitted in one polarization, the serving cell is enabled to be selected based on highest RSRP based on SSBs transmitted in two polarizations. This will reduce the risk of polarization mismatching and hence reduce the risk of erroneous cell selection for the terminal device150. Since the terminal device150is configured to average the mobility measurements over multiple SSB bursts (as long as the parameter “a” in Equation 1 is smaller than 1), the terminal device150will obtain a value of the RSRP of the SSB that is averaged over two polarization (where how much the RSRP as measured for each polarization is weighted in the averaging depends on the value of “a” in accordance with Equation 1). This will avoid the situation resulting in erroneous cell selection as disclosed above with reference toFIG.3.

Embodiments relating to further details of transmission of synchronization signals as performed by the network node200will now be disclosed.

There may be different ways transmit the SSBs such that one SSB is transmitted per each beam160a:160N in each burst, and the polarization P1, P2 of at least one of the SSBs changes between two consecutive bursts of the SSBs. Different embodiments relating thereto will now be described in turn with reference toFIG.5.

FIG.5schematically illustrates polarizations of SSBs of K bursts of SSBs according to embodiments.

Although illustrated as occurring in order SSB 1, SSB 2, SSB 3, . . . , SSB N this order is given only for illustrative purposes and it could be that SSB n+1 is transmitted before SSB n, where 1≤n<N in each SSB burst. Regardless, the sequence according to which the polarization P1, P2, changes would remain the same as inFIG.5; and the polarizations would then have a different mapping to the SSBs.

In general terms,FIG.5at (a), (b), (c), (d), and (e) illustrate five scenarios according to which the polarization of the SSBs might change; either only between consecutive bursts of SSBs (as in scenario (a)), or only between consecutive individual SSBs within each burst of SSBs (as in scenario (b)), or between both consecutive bursts of SSBs and between consecutive individual SSBs within each burst of SSBs (as in scenario (d)), or according to other rules (as in scenarios (c) and (e)).

In some aspects there is one change of polarization P1, P2 per burst of SSBs. That is according to an example, the polarization P1, P2 changes only between consecutive bursts. Accordingly, all SSBs within each burst are transmitted with same polarization P1, P2, and the SSBs of two consecutive bursts collectively are transmitted with two mutually different polarizations P1, P2. This is the case for scenario (a).

In some aspects there is a change of polarization P1, P2 for each SSB within each burst. That is, according to an example, the polarization P1, P2 changes per every SSB within each burst. Accordingly, within each burst, two consecutive SSBs collectively are transmitted with two mutually different polarizations P1, P2. This is the case for scenario (b) as well as for scenario (d).

In some aspects there is a change of polarization P1, P2 in every second beam. That is, according to an example, the polarization P1, P2 changes exactly once per pair of SSBs. Accordingly, within each burst, pairs of consecutive SSBs collectively are transmitted with two mutually different polarizations P1, P2, and the SSBs within each pair are transmitted with same polarization P1, P2. This is the case for scenario (c).

In some aspects there is a change of polarization P1, P2 in any given beam from burst to burst. That is, according to an example, the polarization P1, P2 changes per beam160a:160N from one burst to the next burst. Accordingly, the polarization P1, P2 for each SSB in each burst is different between two consecutive bursts. This is the case for scenarios (a), (d), (e).

In some aspects there is a change of polarization P1, P2 in every beam, and a change of polarization P1, P2 in any given beam from burst to burst—scenario. That is, according to an example, within each burst, two consecutive SSBs collectively are transmitted with two mutually different polarizations P1, P2, and wherein the polarization P1, P2 for each SSB in each burst is different between two consecutive bursts. This is the case for scenario (d).

In some aspects there is a change of polarization P1, P2 in every second beam, and a change of polarization in any given beam from burst to burst. That is, according to an example, within each burst, pairs of consecutive SSBs collectively are transmitted with two mutually different polarizations P1, P2, wherein the SSBs within each pair are transmitted with same polarization P1, P2, and wherein the polarization P1, P2 for each SSB in each burst is different between two consecutive bursts. This is the case for scenario (e).

In some aspects, when considering all SSBs of two consecutive bursts of SSBs, half of the SSBs are transmitted with polarization P1 and the remaining half of the SSBs are transmitted with polarization P2.

In some aspects the network node200is configured to perform two-dimensional beamforming. In other words, the beams16omight be part of a two-dimensional grid of beams. The network node200might then transmit two-dimensional bursts of SSBs. Particularly, in some examples, the polarized bursts of SSB are transmitted in vertically oriented beams16oand in horizontally oriented beams160, whereby two-dimensional bursts of SSBs are transmitted. SSBs in beams16oneighbouring each other in horizontal as well as in vertical orientation might collectively be transmitted with two mutually different polarizations P1, P2.

In some aspects the two mutually different polarizations P1, P2 are orthogonal with respect to each other.

The optimal value of the filter coefficient “a” in Equation 1 might be different depending on if one single polarization is used for all SSBs and all SSB bursts or if different polarizations are used between different SSBs and/or SSB bursts. In the latter case, the terminal device150might measure SSBs on two more or less independent radio propagation channels (assuming that SSBs transmitted with both polarizations are received by the terminal device150), which means that it might be more optimal to increase the value of “a” compared to if only a single polarization is used for the transmission of the SSB. That is, in some aspects the value of “a” is changed such that the cell-selection criteria is calculated with more consideration to previous measurements when the herein disclosed embodiments are used for transmission of synchronization signals, such as SSBs.

One particular embodiment for transmission of synchronization signals as performed by the network node200will now be disclosed with reference to the signalling diagram ofFIG.6. S201: The network node200transmits a burst of SSBs using a first polarization P1.

One way to implement step S201is to perform step S102.

S202: The terminal device150receives the SSB and performs measurements of RSRP on the SSS of the SSB. The terminal device150then adds the latest measurements to the filtered mobility measurements using Equation 1 with “a” modified as disclosed above.

S203: The network node200transmits the next SSB burst, but changes the polarization to a second polarization P2 that is orthogonal to the first polarization P1.

One way to implement step S203is to perform step S102.

S204: The terminal device150receives the SSB and performs measurements of RSRP on the SSS of the SSB. The terminal device150then adds the latest measurements to the filtered mobility measurements using Equation 1 with “a” modified as disclosed above.

Step S201might then be entered again.

In view of the above, the transmission of synchronization signals is here thus based on scenario (a) ofFIG.5. However, the skilled person would, in view of the present disclosure, understand how to modify the method defined by steps S201-S204for each respective scenario (b), (c), (d), and (e) ofFIG.5.

Thus the processing circuitry210is thereby arranged to execute methods as herein disclosed. The storage medium230may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The network node200may further comprise a communications interface220at least configured for communications with other entities, functions, nodes and devices of the communications network100a,100b. As such the communications interface220may comprise one or more transmitters and receivers, comprising analogue and digital components. The processing circuitry210controls the general operation of the network node200e.g. by sending data and control signals to the communications interface220and the storage medium230, by receiving data and reports from the communications interface220, and by retrieving data and instructions from the storage medium230. Other components, as well as the related functionality, of the network node200are omitted in order not to obscure the concepts presented herein.

FIG.8schematically illustrates, in terms of a number of functional modules, the components of a network node200according to an embodiment. The network node200ofFIG.8comprises a transmit module210aconfigured to perform step S102. The network node200ofFIG.8may further comprise a number of optional functional modules as schematically illustrated by functional module210b. In general terms, each functional module210a-210bmay in one embodiment be implemented only in hardware and in another embodiment with the help of software, i.e., the latter embodiment having computer program instructions stored on the storage medium230which when run on the processing circuitry makes the network node200perform the corresponding steps mentioned above in conjunction withFIG.8. It should also be mentioned that even though the modules correspond to parts of a computer program, they do not need to be separate modules therein, but the way in which they are implemented in software is dependent on the programming language used. Preferably, one or more or all functional modules210a-210bmay be implemented by the processing circuitry210, possibly in cooperation with the communications interface220and/or the storage medium230. The processing circuitry210may thus be configured to from the storage medium230fetch instructions as provided by a functional module210a-210band to execute these instructions, thereby performing any steps as disclosed herein.

The network node200may be provided as a standalone device or as a part of at least one further device. For example, the network node200may be provided in a node of the radio access network110or in a node of the core network120. Alternatively, functionality of the network node200may be distributed between at least two devices, or nodes. These at least two nodes, or devices, may either be part of the same network part (such as the radio access network110or the core network120) or may be spread between at least two such network parts. In general terms, instructions that are required to be performed in real time may be performed in a device, or node, operatively closer to the cell than instructions that are not required to be performed in real time.

Thus, a first portion of the instructions performed by the network node200may be executed in a first device, and a second portion of the of the instructions performed by the network node200may be executed in a second device; the herein disclosed embodiments are not limited to any particular number of devices on which the instructions performed by the network node200may be executed. Hence, the methods according to the herein disclosed embodiments are suitable to be performed by a network node200residing in a cloud computational environment. Therefore, although a single processing circuitry210is illustrated inFIG.7the processing circuitry210may be distributed among a plurality of devices, or nodes. The same applies to the functional modules210a-210bofFIG.8and the computer program920ofFIG.9.

FIG.9shows one example of a computer program product910comprising computer readable storage medium930. On this computer readable storage medium930, a computer program920can be stored, which computer program920can cause the processing circuitry210and thereto operatively coupled entities and devices, such as the communications interface220and the storage medium230, to execute methods according to embodiments described herein. The computer program920and/or computer program product910may thus provide means for performing any steps as herein disclosed.

FIG.10is a schematic diagram illustrating a telecommunication network connected via an intermediate network420to a host computer430in accordance with some embodiments. In accordance with an embodiment, a communication system includes telecommunication network410, such as a 3GPP-type cellular network, which comprises access network411, such as radio access network110inFIG.1, and core network414, such as core network120inFIG.1. Access network411comprises a plurality of radio access network nodes412a,412b,412c, such as NBs, eNBs, gNBs (each corresponding to the network node200ofFIG.1) or other types of wireless access points, each defining a corresponding coverage area, or cell,413a,413b,413c. Each radio access network nodes412a,412b,412cis connectable to core network414over a wired or wireless connection415. A first UE491located in coverage area413cis configured to wirelessly connect to, or be paged by, the corresponding network node412c. A second UE492in coverage area413ais wirelessly connectable to the corresponding network node412a. While a plurality of UE491,492are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole terminal device is connecting to the corresponding network node412. The UEs491,492correspond to the terminal device150ofFIG.1.

Telecommunication network410is itself connected to host computer430, which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server or as processing resources in a server farm.

Host computer430may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider.

Connections421and422between telecommunication network410and host computer430may extend directly from core network414to host computer430or may go via an optional intermediate network420. Intermediate network420may be one of, or a combination of more than one of, a public, private or hosted network; intermediate network420, if any, may be a backbone network or the Internet; in particular, intermediate network420may comprise two or more sub-networks (not shown).

Communication system500further includes radio access network node520provided in a telecommunication system and comprising hardware525enabling it to communicate with host computer510and with UE530. The radio access network node520corresponds to the network node200ofFIG.1. Hardware525may include communication interface526for setting up and maintaining a wired or wireless connection with an interface of a different communication device of communication system500, as well as radio interface527for setting up and maintaining at least wireless connection570with UE530located in a coverage area (not shown inFIG.11) served by radio access network node520. Communication interface526may be configured to facilitate connection56oto host computer510. Connection56omay be direct or it may pass through a core network (not shown inFIG.11) of the telecommunication system and/or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, hardware525of radio access network node520further includes processing circuitry528, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. Radio access network node520further has software521stored internally or accessible via an external connection.

It is noted that host computer510, radio access network node520and UE530illustrated inFIG.11may be similar or identical to host computer430, one of network nodes412a,412b,412eand one of UEs491,492ofFIG.10, respectively. This is to say, the inner workings of these entities may be as shown inFIG.11and independently, the surrounding network topology may be that ofFIG.10.

Wireless connection570between UE530and radio access network node520is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to UE530using OTT connection550, in which wireless connection570forms the last segment. More precisely, the teachings of these embodiments may reduce interference, due to improved classification ability of airborne UEs which can generate significant interference.