UE-SIDE BEAM SELECTION PROCEDURE

There is provided mechanisms for assisting a UE-side beam selection procedure. A method is performed by a network node. The method comprises estimating TRP-side angular information of a CE from uplink signalling received from the UE at a TRP of the network node. The method comprises reporting the TRP-side angular 5 information towards the UE and configuring the UE to perform a UE-side beam selection procedure based on the TRP-side angular information.

TECHNICAL FIELD

Embodiments presented herein relate to a method, a network node, a computer program, and a computer program product for assisting a UE-side beam selection procedure. Embodiments presented herein further relate to a method, a user equipment, a computer program, and a computer program product for performing a UE-side beam selection procedure.

BACKGROUND

In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.

For example, for future generations of mobile communications networks, frequency bands at many different carrier frequencies could be needed. For example, low such frequency bands could be needed to achieve sufficient network coverage for wireless devices and higher frequency bands (e.g. at millimeter wavelengths (mmW), i.e. near and above 30 GHz, or even frequency bands in the THz, or at least sub-THz region) could be needed to reach required network capacity. In general terms, at high frequencies the propagation properties of the radio channel are more challenging and beamforming both at the network node of the network and at the wireless devices might be required to reach a sufficient link budget.

FIG.1is a schematic diagram illustrating a communication network100according to an example. The communication network100could be a fourth generation (4G) telecommunications network, a fifth generation (5G) telecommunications network, or any evolvement thereof, and support any 3rd generation partnership project (3GPP) telecommunications standard, where applicable.

The communication network100comprises a network node200configured to provide network access to user equipment (UE), as represented by UE300, in 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 UE300is 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 UE300is configured to communicate with each other over wireless links190in a radio propagation channel, or environment. Examples of network nodes200are radio access network nodes, radio base stations, base transceiver stations, Node Bs (NBs), evolved Node Bs (eNBs), gNBs, access points, access nodes, and integrated access and backhaul (IAB) nodes. Examples of UEs300are wireless devices, mobile stations, mobile phones, handsets, wireless local loop phones, smartphones, laptop computers, tablet computers, network equipped sensors, network equipped vehicles, and so-called Internet of Things devices.

Due to severe propagation losses, the radio propagation channel in such high frequency bands usually have a few useful paths, or even just the line of sight (LOS) path, for facilitating reliable communication between TRP at the network-side and a UE at the user-side. Large antenna arrays are then used to provide array gains large enough to overcome the propagation losses. However, large antenna arrays operating at higher frequency bands generally have only few radio-frequency (RF) chains due to hardware complexity. This allows only for the use of analog or hybrid beamforming. In this case, beams are narrow and time multiplexed, yielding a very large number of beams to be managed at both the network-side and the user-side.

In this context, beam management as used in new radio (NR) telecommunication systems, also referred to as 5G telecommunication systems, includes some procedures that are mainly responsible for i) establishing an initial beam pair link (BPL) between the TRP and the UE, and ii) maintaining the BPL with good quality. A beam refinement procedure can then be performed to improve link quality, for example by finding BPLs with beams (at both the TRP and the UE) that provide higher array gain and/or better spatial alignment than the initial BPL. However, in such higher frequency bands, large bandwidth and high throughput make session time short. Therefore, the beam refinement procedure must be fast to be useful. This will be further elaborated on with reference toFIG.2.FIG.2schematically illustrates a beam management procedure, which is a typical example of a legacy NR beam management procedure, consisting of three sub-procedures, referred to as P-1, P-2, and P-3sub-procedures. These three sub-procedures will now be disclosed in more detail.

One main purpose of the P-1sub-procedure is for the network node200to find a coarse direction towards the UE300by transmitting reference signals in wide, but narrower than sector, beams that are swept over the whole angular sector. The TRP140is expected to, for the P-1sub-procedure, utilize beams, according to a spatial beam pattern150a, with rather large beam widths. During the P-1sub-procedure, the reference signals are typically transmitted periodically and are shared between all UEs300served by the network node200in the radio access network110. The UE300uses a wide, or even omni-directional beam for receiving the reference signals during the P-1sub-procedure, according to a spatial beam pattern172a. The reference signals might be periodically transmitted channel state information reference signals (CSI-RS) or synchronization signal blocks (SSB). The UE300might then to the network node200report the N≥1 best beams and their corresponding quality values, such as reference signal received power (RSRP) values. The beam reporting from the UE300to the network node200might be performed rather seldom (in order to save overhead) and can be either periodic, semi-persistent or aperiodic.

One main purpose of the P-2sub-procedure is to refine the beam selection at the TRP140by the network node200transmitting reference signals whilst performing a new beam sweep with more narrow directional beams, according to a spatial beam pattern160a, than those beams used during the P-1sub-procedure, where the new beam sweep is performed around the coarse direction, or beam, reported during the P-1sub-procedure. During the P-2sub-procedure, the UE300typically uses the same beam as during the P-1sub-procedure, according to a spatial beam pattern172a. The UE300might then to the network node200report the N≥1 best beams and their corresponding quality values, such as reference signal received power (RSRP) values. One P-2sub-procedure might be performed per each UE300or per each group of terminal devices200. The reference signals might be aperiodically or semi-persistently transmitted CSI-RS. The P-2sub-procedure might be performed more frequently than the P-1sub-procedure in order to track movements of the UE300and/or changes in the radio propagation environment.

One main purpose of the P-3sub-procedure is for UEs300utilizing analog beamforming, or digital wideband (time domain beamformed) beamforming, to find best beam. During the P-3sub-procedure, the reference signals are transmitted, according to a spatial beam pattern162a, in the best reported beam of the P-2sub-procedure whilst the UE300performs a beam sweep, according to a spatial beam pattern180a. The P-3sub-procedure might be performed at least as frequently as the P-2sub-procedure in order to enable the UE300to compensate for blocking, and/or rotation.

In general, the beam management is based on the transmission of reference signals (RSs) in different directional beams in a set of pre-specified intervals and directions to cover a spatial area. As the number of candidate BPLs to evaluate can be comparatively large, the beam refinement procedure might require longer time to be performed than desired.

Hence, there is still a need for improved beam selection procedures.

SUMMARY

An object of embodiments herein is to provide efficient beam selection at the UE.

According to a first aspect there is presented a method for assisting a UE-side beam selection procedure. The method is performed by a network node. The method comprises estimating TRP-side angular information of a UE from uplink signalling received from the UE at a TRP of the network node. The method comprises reporting the TRP-side angular information towards the UE and configuring the UE to perform a UE-side beam selection procedure based on the TRP-side angular information.

According to a second aspect there is presented a network node for assisting a UE-side beam selection procedure. The network node comprises processing circuitry. The processing circuitry is configured to cause the network node to estimate TRP-side angular information of a UE from uplink signalling received from the UE at a TRP of the network node. The processing circuitry is configured to cause the network node to report the TRP-side angular information towards the UE and configuring the UE to perform a UE-side beam selection procedure based on the TRP-side angular information.

According to a third aspect there is presented a network node for assisting a UE-side beam selection procedure. The network node comprises an estimate module configured to estimate TRP-side angular information of a UE from uplink signalling received from the UE at a TRP of the network node. The network node comprises a report module configured to report the TRP-side angular information towards the UE and configuring the UE to perform a UE-side beam selection procedure based on the TRP-side angular information.

According to a fourth aspect there is presented a computer program for assisting a UE-side beam selection procedure, the computer program comprising computer program code which, when run on processing circuitry of 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 method for performing a UE-side beam selection procedure. The method is performed by a UE. The method comprises transmitting uplink signalling towards a TRP of a network node. The method comprises receiving, from the network node, reporting of TRP-side angular information of the UE from the uplink signalling and configuration for the UE to perform a UE-side beam selection procedure based on the TRP-side angular information. The method comprises selecting, as part of performing the UE-side beam selection procedure, a beam to use for communication with the TRP. The beam has a pointing direction that is selected as a function of the TRP-side angular information.

According to a sixth aspect there is presented a UE for performing a UE-side beam selection procedure. The UE comprises processing circuitry. The processing circuitry is configured to cause the UE to transmit uplink signalling towards a TRP of a network node. The processing circuitry is configured to cause the UE to receive, from the network node, reporting of TRP-side angular information of the UE from the uplink signalling and configuration for the UE to perform a UE-side beam selection procedure based on the TRP-side angular information. The processing circuitry is configured to cause the UE to select, as part of performing the UE-side beam selection procedure, a beam to use for communication with the TRP. The beam has a pointing direction that is selected as a function of the TRP-side angular information.

According to a seventh aspect there is presented a UE for performing a UE-side beam selection procedure. The UE comprises a transmit module configured to transmit uplink signalling towards a TRP of a network node. The UE comprises a receive module configured to receive, from the network node, reporting of TRP-side angular information of the UE from the uplink signalling and configuration for the UE to perform a UE-side beam selection procedure based on the TRP-side angular information. The UE comprises a select module configured to select, as part of performing the UE-side beam selection procedure, a beam to use for communication with the TRP. The beam has a pointing direction that is selected as a function of the TRP-side angular information.

According to an eighth aspect there is presented a computer program for performing a UE-side beam selection procedure, the computer program comprising computer program code which, when run on processing circuitry of a UE, causes the UE to perform a method according to the fifth aspect.

According to a ninth aspect there is presented a computer program product comprising a computer program according to at least one of the fourth aspect and the eighth 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.

According to a tenth aspect there is presented a system. The system comprises a network node according to any of the second or third aspects and a UE according to any of the sixth or seventh aspects.

Advantageously, these aspects enable the UE to perform a beam selection procedure based on angular information obtained at the TRP and reported from the TRP to the UE.

Advantageously, according to these aspects, the UE does not need to perform a beam sweeping procedure as in the legacy NR beam management P-3sub-procedure to obtain beam quality information. In turn, this will save UE energy by avoiding multiple transmissions of reference signals in the downlink or multiple transmissions of reference signals in the uplink.

Advantageously, according to these aspects, the UE is enabled to select a refined, or narrower, beam at shorter delay due to the fact that no beam sweeping is needed.

Advantageously, according to these aspects, the UE does not need to perform any angle estimation procedure to obtain angular information for the purpose of beam refinement. In turn, this will save UE energy.

Advantageously, according to these aspects, the UE is enabled to update its beam separately in the azimuth domain or in the zenith domain or in both domains, depending on how fast the TRP-side angular information changes in each domain. In turn, this can save the use of the downlink feedback channel used by the network node to report the TRP-side angular information to the UE.

Advantageously, according to these aspects, the estimation of the angular information is performed by the network node which generally has a larger antenna array (and more available computational power) than the UE, enabling the estimation to be more accurate.

DETAILED DESCRIPTION

As disclosed above, there is still a need for improved beam selection procedures. In this respect, the legacy NR beam management procedure disclosed above with reference toFIG.2, after the initial BPL establishment (in the P-1sub-procedure), the network node200and the UE300need to select a subset of narrow beams for the P-2and P-3sub-procedure. When the number of beams is very large, which is the case in higher frequency bands due to the use of very large antenna arrays, few beams should be selected to be swept in order to have a reasonable latency. However, knowing which beams to be used in the beam sweeping procedure becomes particularly challenging as the beams become narrower.

Angular information of the LOS path can suffice for the beams to be updated during the management procedures. This motivates the development of angular-based beam management procedures. In this respect, the channel state of the radio propagation channel between the TRP140and the UE300depends, among other things, on the relative geographical positions and orientations of the TRP140and the UE300. In 3GPP TR 38. 901 “Study on channel model for frequencies from 0.5 to 100 GHz”, version 16.1.0, a common positioning system defined by coordinates in a Cartesian coordinate system, the spherical angles, and the spherical unit vector called a global coordinate system (GCS) is adopted, as shown inFIG.3. In particular,FIG.3shows definition of spherical angles and spherical unit vectors in a Cartesian coordinate system, where n is the given direction, and where § and Ô are the spherical basis vectors.

An orientation-based beam management procedure might rely on the estimation of the angle-of-arrival (AoA) and/or angle-of-departure (AoD) for some signals transmitted between the TRP140and the UE300. Given the angle estimate (in terms of angle-of-arrival or angle-of-departure), beams to be used both at the TRP140and the UE300can be refined, or updated, as in the P-2or P-3sub-procedures by at each side finding the most spatially aligned beam with the estimated angle.

However, the procedure for estimating the angle-of-arrival and the procedure for estimating the angle-of-departure require an independent procedure to be performed at each side; one is performed at the UE300for determining the UE-side beam and another is performed at the network node200for determining the TRP-side beam. That is, the UE-side beam refinement, or update, does not benefit from any angular information obtained by the network node200.

The embodiments disclosed herein therefore relate to mechanisms for assisting a UE-side beam selection procedure and for performing a UE-side beam selection procedure. 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 processing circuitry of the network node200, causes the network node200to perform the method. In order to obtain such mechanisms there is further provided a UE300, a method performed by the UE300, and a computer program product comprising code, for example in the form of a computer program, that when run on processing circuitry of the UE300, causes the UE300to perform the method.

Reference is now made toFIG.4illustrating a method for assisting a UE-side beam selection procedure as performed by the network node200according to an embodiment.

S102: The network node200estimates TRP-side angular information of the UE300from uplink signalling received from the UE300at a TRP140of the network node200. The TRP-side angular information is thus angular information of the UE300as estimated at the TRP-side.

S104: The network node200reports the TRP-side angular information towards the UE300. Further, the network node200configures the UE300to perform a UE-side beam selection procedure based on the TRP-side angular information.

In that the network node200reports information towards the UE300, the network node200thus feeds back, or otherwise provides, some useful information to the UE300. According to the present disclosure, the useful information would be the TRP-side angular information, of which examples are provided below. This TRP-side angular information is reported to the UE300so that the UE300can use it to select a new beam (i.e., for the UE300to perform a UE-side beam selection procedure. In order for the UE300to know that it indeed should use the reported TRP-side angular information to select a new beam, the UE300needs to receive some indication from the network node200to do so. The network node200therefore configures the UE300to perform the UE-side beam selection procedure based on the TRP-side angular information, as in S104. Further in this respect, and as will be disclosed in more detail below with reference toFIG.4, the UE300might therefore be configured by the network node200to (a) receive the report in some set of resources, e.g., of a shared channel, then (b) handle the reported information properly to eventually select a new beam, and then, optionally, (c) sound the selected beam in the uplink. In order to achieve this, items (a), (b), and (c) can realized as parameters, or fields, of the same control message or can be split into multiple control messages. Particularly, a control message related to item (a) may include the report itself instead of indicating what channel, resources, the report will be sent in. In other words, the content of the report (i.e., TRP-side angular information) could be part of a control message, such as the control message for item (a).

Embodiments relating to further details of assisting a UE-side beam selection procedure as performed by the network node200will now be disclosed.

There could be different examples of TRP-side angular information of the UE300that is estimated by the network node200in S102. In some embodiments the TRP-side angular information is an estimate of angle-of-arrival at the TRP140of the uplink signalling received from the UE300. The network node200might estimate the angle-of-arrival either in the azimuth domain or in the elevation domain, or in both domains, depending on the channel dynamics and/or mobility pattern of the UE300. Particularly, in some embodiments the angle-of-arrival pertains to angle-of-arrival in azimuth, or in elevation, or both azimuth and elevation. In some examples, the network node200configures the UE300with a different beam selection periodicity in each angle domain. In some cases, it is of interest to refine the beam selection at the UE300in both angle domains, and thus that the TRP-side angular information is defined in both azimuth and elevation domain. In other cases, the angular characteristics of the radio propagation channel varies faster in one angle domain than in the other angle domain, and thus the TRP-side angular information with the angle domain that varies faster should be reported more frequently.

There could be different ways in which the network node200estimates the TRP-side angular information of the UE300from the uplink signalling received from the UE300. In some aspects, the network node200estimates the TRP-side angular information that characterizes the radio propagation channel between the UE300and the TRP140through a set of reference signals transmitted by the UE300in the uplink. Particularly, in some embodiments the TRP-side angular information of the UE300is estimated from uplink signalling in terms of a set of reference signals. The reference signals might be sounding reference signals (SRS), as defined by 3GPP. Any combination of uplink reference signal transmission and angle estimation technique can be adopted for the purpose of obtaining the TRP-side angular information. Any other combination also considering downlink reference signal transmissions can also be adopted for the same purpose.

In some aspects, the network node200configures the UE300to update its beam in azimuth domain or in elevation domain, either separately or jointly in both domains. As an example, the network node200might transmit a downlink control message to the UE300to configure the UE300to perform the UE-side beam selection procedure. Particularly, in some embodiments the UE300is by the network node200configured to perform the UE-side beam selection procedure only in azimuth domain, only in elevation domain, or in both azimuth and elevation domains. The control message might further indicate downlink resources in which the UE300will receive the TRP-side angular information. The control message might further indicate to the UE300the type of TRP-side angular information that will be reported; an azimuth angle, an elevation angle, or both an azimuth angle and an elevation angle. The control message might further indicate to the UE300what coordinate system the TRP-side angular information is defined in. In some cases, there might be a list of coordinate systems in which the TRP-side angular information can be defined. In some other cases, there is a single reference coordinate system already known by both the network node200and the UE300, which dismiss the need for any coordinate system indication.

In some aspects, the network node200transmits a control message that indicates that uplink sounding with the beam as selected by the UE300is needed. Particularly, in some embodiments, the network node200is configured to perform (optional) step S106:

S106: The network node200transmits a control message towards the UE300. The control message indicates that the UE300is to perform uplink sounding using a beam selected by the UE300as part of performing UE-side beam selection procedure.

Hence, a control message might be transmitted by the network node200that indicates to the UE300whether an uplink sounding with the beam as selected by the UE300is needed. If such an uplink sounding is indicated as needed, the control message might also indicate configured uplink resources for the UE300to use for transmission of an uplink sounding signal with the beam as selected by the UE300.

As will be disclosed below, the UE300might then use the selected beam when transmitting an uplink signalling for uplink sounding. Hence, in some aspects, the network node200receives a beamformed sounding signal from the UE300in a configured set of uplink resources. Therefore, the UE300might by the network node200be configured to transmit uplink signalling for uplink sounding in this configured set of uplink resources. In some embodiments, the network node200is therefore configured to perform (optional) step S108:

S108: The network node200receives uplink signalling for uplink sounding from the UE300using the beam selected by the UE300.

In some examples, the network node200evaluates the uplink signalling by measuring the corresponding beam quality in terms of layer1reference signal received power (L1-RSRP). Other Li measurements, or even higher layer measurements, can be adopted for the same purpose.

After having evaluated the quality of the beam selected by the UE300, the network node200might transmit a beam adjustment indication for the UE300to either use the new beam or to keep a previous or current beam. In some aspects, the new beam should be used if it provides a BPL with better quality compared to the BPL with the previous or current beam. In some aspects, upon reception and evaluation of the uplink signalling, the network node200might thus determine and transmit to the UE300a beam adjustment indicator based on the previously measured beamformed sounding signal. In some embodiments, the network node200is therefore configured to perform (optional) step S110:

S110: The network node200transmits a beam adjustment indicator towards the UE300.

In some embodiments, the beam adjustment indicator is transmitted only when received power of the uplink signalling is more than a threshold value lower than received power of previously received uplink signalling from the UE300. However, in other embodiments, the beam adjustment indicator is always transmitted to inform the UE300whether or not to keep the selected beam in which the UE transmitted the uplink signal.

Reference is now made toFIG.5illustrating a method for performing a UE-side beam selection procedure as performed by the UE300according to an embodiment.

S202: The UE transmits uplink signalling towards the TRP140of the network node200. In some embodiments, the uplink signalling is transmitted in terms of a set of reference signals. Different reference signals can be adopted for the same purpose.

S204: The UE300receives, from the network node200, reporting of TRP-side angular information of the UE300from the uplink signalling. The UE300further receives configuration for the UE300to perform a UE-side beam selection procedure based on the TRP-side angular information.

S206: The UE300selects, as part of performing the UE-side beam selection procedure, a beam to use for communication with the TRP140. The beam has a pointing direction that is selected as a function of the TRP-side angular information.

This procedure can be carried out for the UE300to find a narrower beam within the angular space covered by a given wider beam that is currently used by the UE300. Assume that the UE300is using a wide beam covering the angular interval [0,20] (in degree) in azimuth, for instance. Then, a refined, or narrower beam, could be selected within this interval, say covering [5,10] in azimuth, for instance. Such a refined, or narrower beam, could have a larger beam gain within the narrower angular interval than the wide beam. Hence, with reference toFIG.2, this procedure could be used by the UE300in the P-3sub-procedure. In fact, this procedure could replace the actions taken by the UE300in the P-3sub-procedure.

Embodiments relating to further details of performing a UE-side beam selection procedure as performed by the UE300will now be disclosed.

As further disclosed above, the network node200might estimate the angle-of-arrival either in the azimuth domain or in the elevation domain, or in both domains, depending on the channel dynamics and/or mobility pattern of the UE300. Particularly, in some embodiments the angle-of-arrival pertains to angle-of-arrival in azimuth, or in elevation, or both azimuth and elevation.

In some aspects, the UE300transforms the received TRP-side angular information to its own coordinate system, considering the coordinate system in which the TRP-side angular information is defined. Particularly, in some embodiments the TRP-side angular information is defined in a first coordinate system, the beam is selected in a second coordinate system, and the UE300as part of selecting the beam transforms the TRP-side angular information to the second coordinate system. There could be different examples of the first coordinate system and the second coordinate system. Particularly, in some embodiments the TRP140is oriented with respect to the first coordinate system and the UE300is oriented with respect to the second coordinate system. The first coordinate system might be a global coordinate system (GCS), and the second coordinate system might be a local coordinate system (LCS). In further detail, an antenna array at the UE300can be oriented with respect the LCS that has the center of the antenna array as the origin of LCS, which is used as a reference to define the far-field. The reference directions in the LCS will depend on the orientation of the antenna array, which varies with the orientation of the UE300. Angular information regarding rays/paths, i.e., angle-of-arrival and angle-of-departure, can be characterized in terms of either the GCS or LCS. The LCS can be determined by a sequence of rotation angles (a, B and y) regarding axes (x, y and z) over the GCS. The TRP-side angular information might thus be transformed from the first coordinate system to the second coordinate system according to a relation between the first coordinate system and the second coordinate system, and wherein the relation is determined by the UE300.

As disclosed above, a control message as transmitted by the network node200might indicate to the UE300what coordinate system the TRP-side angular information is defined in. Particularly, in some embodiments the relation is determined from information defining the first coordinate system as received in a control message from the network node200.

In some aspects, the relation between the first coordinate system and the second coordinate system can be determined based on rotational information. Particularly, in some embodiments the relation is determined from a rotation of the UE300, with respect to the first coordinate system, as locally obtained by the UE300.

The LCS rotation angles can be used to characterize the UE and/or TRP rotation matrices, as in Equation (1):

The transformation R can be used to convert coordinates from the LCS to the GCS. The reverse transformation R−1, i.e., to convert coordinates from the GCS to the LCS, and thus to transform the TRP-side angular information to UE-side angular information, is equal to the transpose of R. That is, R−1=RT.

Rotational information thus can be used by the UE300to transform the received TRP-side angular information to its LCS. Such rotational information can be obtained for example from an inertial measurement unit (IMU) that can be an accelerometer, gyroscopes, or magnetometers.

Assume further that the network node200also has its own LCS (which is different from both the GCS and the LCS of the UE300) and that the network node200first estimates the TRP-side angular information in its own LCS. In case of a single LOS path scenario, let (ϕLOS′, θLOS′) be angles-of-arrival obtained by the network node200in its own LCS. The network node200can then transform the TRP-side angular information from its own LCS to a reference GCS in two steps. First, both angles (ϕLOS′, θLOS′) are transformed to the GCS using the matrix R in Equation (2), as follows:

Second, the angles in the GCS (ϕLOS, θLOS) are obtained from Equation (2) according to Equations (3) and (4):

The TRP-side angular information (ϕLOS,trp, θLOS,trp) can be used by the UE300to obtain UE-side angular information (ϕLOS,UE, θLOS,UE) in the GCS according to Equations (5) and (6):

Finally, the UE300transforms the pair of angles in Equations (5) and (6) into its own LCS using Equations (7), (8), and (9):

The UE300thus selects a new UE-side beam, as in S206, based on the received TRP-side angular information transformed into its LCS.

In some aspects, the UE300selects the beam being most spatially aligned with the angle-of-arrival. Particularly, in some embodiments the beam is selected to, according to a given metric, have an angle-of-departure that is spatially aligned with the angle-of-arrival.

In general terms, the beam selected by the UE300in S206can be represented by a vector of complex-valued weights that shift the phase and/or amplitude of signals in each antenna element of the antenna array at the UE300. This weight vector (or simply beam vector) can be designed in order to radiate energy towards an intended spatial direction (e.g., pair of azimuth and zenith angles). A steering vector function can be used to map a pair of azimuth and zenith angles to a beam vector. The steering vector function also depends on the wavelength and antenna element positions. However, in some cases, a beam pointing to an intended direction cannot be realized in practice due to hardware limitations. In this context, a grid of beams, i.e., a set of feasible beam vectors, could be adopted. Then, one out of such beam vectors should be selected. The selection criterion, or metric as referred to above, might be based on some spatial alignment criterion, such as cross-correlation between the beam pointing to an intended direction and the feasible beam vectors. According to the metric, the feasible beam vector that yields the highest cross-correlation is be selected. For a grid-of-beam, the selection can be simplified by using known per beam angle information. For example, the beam with closest bore sight pointing direction, e.g. smallest angle difference compared to a desired direction (as given by the TRP-angular information), can be selected. Or the Half Power Beam Width (HPBW; defined as the reduction by 3 dB from the peak gain) angle range, for example the beam with angle range with largest angle coverage beyond the desired direction, can be selected.

As disclosed above, there could be different examples of TRP-side angular information of the UE300. Particularly, in some embodiments the TRP-side angular information is an estimate of angle-of-arrival at the TRP140of the uplink signalling transmitted by the UE300. In some aspects, the UE300is configured by the network node200to update its beam in azimuth domain or in elevation domain, either separately or jointly in both domains. Particularly, in some embodiments the UE300is configured to perform the UE-side beam selection procedure only in azimuth domain, only in elevation domain, or in both azimuth and elevation domains. In some examples, the spatial characteristics of the beam as selected in S206differ from a previous or current UE-side beam in both azimuth and elevation domains if the received TRP-side angular information comprises both domains. In other examples, the spatial characteristics of the beam as selected in S206differ from the previous or current UE-side beam only in the azimuth domain, whilst the characteristics in the elevation domain are kept as in the previous or current UE-side beam. In yet other examples, the spatial characteristics of the beam as selected in S206differ from the previous or current UE-side beam only in the elevation domain, whilst the characteristics in the azimuth domain are kept as in the previous or current UE-side beam.

As disclosed above, the network node200might transmit a control message that indicates that uplink sounding with the beam as selected by the UE300is needed. In some embodiments, the UE300is therefore configured to perform (optional) step S208:

S208: The UE300receives a control message from the network node200. The control message indicates that the UE300is to perform uplink sounding using the beam selected by the UE300.

The UE300might then transmit uplink signalling in accordance with the control message received from the network node200in S208. Therefore, in some embodiments, the UE300is configured to perform (optional) step S210:

S210: The UE300transmits uplink signalling for uplink sounding in the beam selected by the UE300.

The uplink signalling might comprise uplink reference signals, such as one or more sounding reference signals. Different reference signals can be adopted for the same purpose.

As disclosed above, the network node200might transmit a beam adjustment indication for the UE300to either use the new beam or to keep a previous or current beam. Therefore, in some embodiments, the UE300is configured to perform (optional) steps S212and S214:

S212: The UE300receives a beam adjustment indicator from the network node200.

S214: The UE300inactivates the beam selected by the UE300from communication with the TRP140when the beam adjustment indicator indicates that received power of the uplink signalling is more than a threshold value lower than received power of previously received uplink signalling from the UE300.

FIG.6schematically illustrates an example of angle correspondence between angle-of-arrival (at the TRP140) and angle-of-departure (at the UE300) of a LOS propagation path between the TRP140and the UE300. For simplicity of illustration but without loss of generality, both the angle-of-arrival and the angle-of-departure are in the azimuth domain (i.e., the XY plane). The x-axis and the y-axis are in a common GCS, whilst the x′-axis and the y′-axis are in the LCS of the UE300. For simplicity, the TRP's LCS is aligned with the GCS. The UE300is rotated around the y-axis by β=π. The UE's300rotation around the y-axis thus shifts its x′-axis to the opposite direction of the x-axis. The angle-of-arrival ϕLOS,UE′ in the LCS of the UE300can be determined from the angle-of-arrival ϕLOS,TRPin the GCS as long as the rotation angle β is known, or can be determined or at least estimated by the UE300and/or the network node200.

One particular embodiment for assisting a UE-side beam selection procedure as performed by the network node200and for performing a UE-side beam selection procedure as performed by the UE300based on at least some of the above disclosed embodiments will now be disclosed in detail with reference to the signalling diagram ofFIG.7.

S301: The network node200reports TRP-side angular information towards the UE300and configures the UE300to perform a UE-side beam selection procedure based on the TRP-side angular information.

S302: The UE300transforms the TRP-side angular information to its own LCS.

S303: The UE300selects, as part of performing the UE-side beam selection procedure, a beam to use for communication with the TRP140of the network node200. The beam has a pointing direction that is selected as a function of the TRP-side angular information (in the LCS of the UE300).

S304: The UE300transmitting, in the beam selected by the UE300, uplink signalling for uplink sounding.

S305: The network node200evaluates the uplink signalling and determines a beam adjustment indicator.

S306: The network node200transmits the beam adjustment indicator towards the UE300.

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 interface220for communications with other entities, functions, nodes, and devices, as inFIG.1. 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.9schematically illustrates, in terms of a number of functional modules, the components of a network node200according to an embodiment. The network node200ofFIG.9comprises a number of functional modules; an estimate module210aconfigured to perform step S102, and a report module210bconfigured to perform step S104. The network node200ofFIG.9may further comprise a number of optional functional modules, such as any of a transmit module210cconfigured to perform step S106, a receive module210dconfigured to perform step S108, and a transmit module210econfigured to perform step S110. In general terms, each functional module210a:210emay be implemented in hardware or in software. Preferably, one or more or all functional modules210a:210emay be implemented by the processing circuitry210, possibly in cooperation with the communications interface220and/or the storage medium230. The processing circuitry210may thus be arranged to from the storage medium230fetch instructions as provided by a functional module210a:210eand to execute these instructions, thereby performing any steps of the network node200as 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 network (such as the TRP140) or in a node of the core network. 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 network or the core network) 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 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.8the processing circuitry210may be distributed among a plurality of devices, or nodes. The same applies to the functional modules210a:210eofFIG.9and the computer program1220aofFIG.12.

FIG.10schematically illustrates, in terms of a number of functional units, the components of a UE300according to an embodiment. Processing circuitry310is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product1210b(as inFIG.12), e.g. in the form of a storage medium330. The processing circuitry310may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

Particularly, the processing circuitry310is configured to cause the UE300to perform a set of operations, or steps, as disclosed above. For example, the storage medium330may store the set of operations, and the processing circuitry310may be configured to retrieve the set of operations from the storage medium330to cause the UE300to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus the processing circuitry310is thereby arranged to execute methods as herein disclosed.

The UE300may further comprise a communications interface320for communications with other entities, functions, nodes, and devices, as inFIG.1. As such the communications interface320may comprise one or more transmitters and receivers, comprising analogue and digital components.

The processing circuitry310controls the general operation of the UE300e.g. by sending data and control signals to the communications interface320and the storage medium330, by receiving data and reports from the communications interface320, and by retrieving data and instructions from the storage medium330. Other components, as well as the related functionality, of the UE300are omitted in order not to obscure the concepts presented herein.

FIG.11schematically illustrates, in terms of a number of functional modules, the components of a UE300according to an embodiment. The UE300ofFIG.11comprises a number of functional modules; a transmit module310aconfigured to perform step S202, a receive module310bconfigured to perform step S204, and a select module310cconfigured to perform step S206. The UE300ofFIG.11may further comprise a number of optional functional modules, such as any of a receive module310dconfigured to perform step S208, a transmit module310econfigured to perform step S210, a receive module310fconfigured to perform step S212, an inactivate module310gconfigured to perform step S214. In general terms, each functional module310a:310gmay be implemented in hardware or in software. Preferably, one or more or all functional modules310a:310gmay be implemented by the processing circuitry310, possibly in cooperation with the communications interface320and/or the storage medium330. The processing circuitry310may thus be arranged to from the storage medium330fetch instructions as provided by a functional module310a:310gand to execute these instructions, thereby performing any steps of the UE300as disclosed herein.

FIG.12shows one example of a computer program product1210a,1210bcomprising computer readable means1230. On this computer readable means1230, a computer program1220acan be stored, which computer program1220acan 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 program1220aand/or computer program product1210amay thus provide means for performing any steps of the network node200as herein disclosed. On this computer readable means1230, a computer program1220bcan be stored, which computer program1220bcan cause the processing circuitry310and thereto operatively coupled entities and devices, such as the communications interface320and the storage medium330, to execute methods according to embodiments described herein. The computer program1220band/or computer program product1210bmay thus provide means for performing any steps of the UE300as herein disclosed.

In the example ofFIG.12, the computer program product1210a,1210bis illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product1210a,1210bcould also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program1220a,1220bis here schematically shown as a track on the depicted optical disk, the computer program1220a,1220bcan be stored in any way which is suitable for the computer program product1210a,1210b.

FIG.13is 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 UE300ofFIG.1.

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.14) served by radio access network node520. Communication interface526may be configured to facilitate connection560to host computer510. Connection560may be direct or it may pass through a core network (not shown inFIG.14) 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.14may be similar or identical to host computer430, one of network nodes412a,412b,412cand one of UEs491,492ofFIG.13, respectively. This is to say, the inner workings of these entities may be as shown inFIG.14and independently, the surrounding network topology may be that ofFIG.13.

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.