Patent Publication Number: US-2023155661-A1

Title: Beam management for a radio transceiver device

Description:
TECHNICAL FIELD 
     Embodiments presented herein relate to a method, a radio transceiver device, a computer program, and a computer program product for beam management. 
     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, one parameter in providing good performance and capacity for a given communications protocol in a communications network is beamforming. 
     For beamforming of data and control signaling, multiple antenna elements are used to amplify the signal in a spatial direction by constructive interference, resulting in a directional gain and thereby a certain beam shape. A predefined setup of such beams is referred to as a Grid of Beams (GoB). 
     The long-term channel properties of deployed radio transceiver devices in, or served by, the network, change for example with mobility, so as a radio transceiver device provided in a user equipment (UE) moves, a radio transceiver device provided in a transmission and reception point (TRP) of the network needs to switch which beam from the GoB to use for data transmissions to the UE. Beam management considers the process of determining a suitable beam to transmit or receive data on. Multiple reference signal measurements and reportings thereof have been standardized to enable beam management. Examples of reference signals suitable for beam management are Channel State Information Reference Signals (CSI-RS) and CSI-RS specifically for Beam Management (CSI-RS-BM). In addition, the UEs can report on a Synchronization Signal Block (SSB) which is periodically transmitted in time on multiple beams. The SSB defines the downlink coverage of the network but since each SSB is associated with a static overhead loss, they may be beamformed with fewer beams than what is used for data. Typical configurations involve forming one or a few wide beams per sector for SSB, whilst beams used for data transmission utilize the full beamforming gain. The spatial footprint, or spatial radiation pattern, of one wide beam might therefore cover the spatial footprints, or spatial radiation patterns, of several narrow beams utilized for data transmission. 
     A radio access network node searches the beam space by, from its TRP, transmitting CSI-RS-BM in candidate beams. The UE is instructed to perform measurements on the beamformed CSI-RS-BM and report up to 4 best quality values (with corresponding CSI-RS-BM resource ID) back to the radio access network node. One such iteration, i.e. the process of transmitting a set of candidate beams and retrieving a corresponding measurement report, is referred to as a beam sweep. Once the beam sweep is complete the radio access network node can decide on which beam to use as a serving data beam for the UE, and which beams to try as beam candidates in the next beam sweep. 
     Typically a beam sweep involves the radio access network node to test a number of beam candidates using a selected scheme that defines which candidate beams to be part of the beam sweep. There could be different types of such schemes, such as random selection of candidate beams, closest neighbor search, transmission of a sparse set of beams, or hierarchical schemes where candidate beams are selected as those covered by the spatial footprint of the best wide beam (given by e.g. SSB reports). 
     Each candidate beam that is to be tested adds an overhead load to the beam management and hence also to the overall system performance. The question of how, and how often, beam management should be performed therefore becomes a trade-off between overhead and performance degradation, where the performance degradation is due to suboptimal beam selection caused by mobility of the UE and/or changes in the radio propagation environment. 
     Hence, there is still a need for improved beam management. 
     SUMMARY 
     An object of embodiments herein is to provide efficient beam management that does not suffer from the issues noted above, or at least where the above noted issues are mitigated or reduced. 
     According to a first aspect there is presented a method for beam management. The method is performed by a radio transceiver device. The method comprises obtaining an angle spread value for signal paths towards a second radio transceiver device. The method comprises performing a beam management procedure for selecting which directional beam to use for communication with the second radio transceiver device by transmitting or receiving reference signals in a candidate set of directional beams. Which directional beams to include in the candidate set of directional beams is dependent on the angle spread value by the angle spread value determining sparsity of the directional beams in the candidate set of directional beams. 
     According to a second aspect there is presented a radio transceiver device for beam management. The radio transceiver device comprises processing circuitry. The processing circuitry is configured to cause the radio transceiver device to obtain an angle spread value for signal paths towards a second radio transceiver device. The processing circuitry is configured to cause the radio transceiver device to perform a beam management procedure for selecting which directional beam to use for communication with the second radio transceiver device by transmitting or receiving reference signals in a candidate set of directional beams. Which directional beams to include in the candidate set of directional beams is dependent on the angle spread value by the angle spread value determining sparsity of the directional beams in the candidate set of directional beams. 
     According to a third aspect there is presented radio transceiver device for beam management. The radio transceiver device comprises an obtain module configured to obtain an angle spread value for signal paths towards a second radio transceiver device. The radio transceiver device comprises a beam management module configured to perform a beam management procedure for selecting which directional beam to use for communication with the second radio transceiver device by transmitting or receiving reference signals in a candidate set of directional beams. Which directional beams to include in the candidate set of directional beams is dependent on the angle spread value by the angle spread value determining sparsity of the directional beams in the candidate set of directional beams. 
     According to a fourth aspect there is presented a computer program for beam management, the computer program comprising computer program code which, when run on a radio transceiver device, causes the radio transceiver device 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 these aspects provide efficient beam management. 
     Advantageously the proposed beam management does not suffer from the issues noted above. 
     Advantageously the proposed beam management provides an additional decision layer that allows for better selection of which scheme that defined which directional beams to include in the candidate set of directional beams at a specific time. 
     Advantageously the proposed beam management enables efficient use of beam management resources, yielding less signaling overhead. 
     Advantageously the proposed beam management enables energy savings whilst causing less interference in neighboring cells from beam sweeps. 
     Advantageously the proposed beam management enables a reduction in interference, which further allows for higher capacity and system performance. 
     Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings. 
     Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the element, apparatus, component, means, module, step, etc.” are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which: 
         FIG.  1    is a schematic diagram illustrating a communication network according to embodiments; 
         FIG.  2    shows cumulative distribution functions of measurements of resulting reference signal received power losses versus the best of all beams in a GoB; 
         FIG.  3    is a flowchart of methods according to embodiments; 
         FIG.  4    schematically illustrates the best reported initial directional beams for a GoB according to an embodiment; 
         FIG.  5    schematically illustrates examples of candidate set of directional beams according to an embodiment; 
         FIG.  6    schematically illustrates beam management procedures performed along a timeline according to an embodiment; 
         FIG.  7    is a schematic diagram showing functional units of a radio transceiver device according to an embodiment; 
         FIG.  8    is a schematic diagram showing functional modules of a radio transceiver device according to an embodiment; 
         FIG.  9    shows one example of a computer program product comprising computer readable storage medium according to an embodiment; 
         FIG.  10    is a schematic diagram illustrating a telecommunication network connected via an intermediate network to a host computer in accordance with some embodiments; and 
         FIG.  11    is a schematic diagram illustrating host computer communicating via a radio base station with a terminal device over a partially wireless connection in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional. 
       FIG.  1    is a schematic diagram illustrating a communication network  100  where embodiments presented herein can be applied. The communication network  100  could be a third generation (3G) telecommunications network, a fourth generation (4G) telecommunications network, a fifth generation (5G) telecommunications network, or any advancement thereof, and support any 3GPP telecommunications standard, where applicable. 
     The communication network  100  comprises a radio access network node  150  configured to provide network access to a user equipment (UE)  160  in a radio access network  110 . The radio access network  110  is operatively connected to a core network  120 . The core network  120  is in turn operatively connected to a service network  130 , such as the Internet. The UE  160  is thereby enabled to access services of the service network  130  and to exchange data with the service network  130 . The operations of accessing services and exchanging data are performed via the radio access network node  150 . The radio access network node  150  comprises, is collocated with, is integrated with, or is in operational communications with, a Transmit and Receive Point (TRP)  140 . 
     Each of the radio access network node  150  and the UE  160  comprises a radio transceiver device  200   a ,  200   b . In the illustrative example of  FIG.  1   , the radio transceiver device  200   a  is part of a radio access network node  150 , and the second radio transceiver device  200   b  is part of a user equipment  160 . However, in other aspects, the radio transceiver device  200   a  is part of a user equipment  160 , and the second radio transceiver device  200   b  is part of a radio access network node  150 . In still further aspects, the radio transceiver device  200   a  is part of a first user equipment  160 , and the second radio transceiver device  200   b  is part of a second user equipment  160 . 
     Examples of radio access network nodes  150  are radio base stations, base transceiver stations, Node Bs (NBs), evolved Node Bs (eNBs), gNBs, access points, access nodes, and backhaul nodes. Examples of UEs  160  are 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. 
     The radio access network node  150  (via its TRP  140 ) and the UE  160  are configured to communicate with each other in directional beams, one of which is illustrated at reference numeral  170 . The directional beam  170  corresponds to a first path  180   a  between the TRP  140  and the UE  160 . However, there might be further paths, such as paths  180   b ,  180   c ,  180   d  between the TRP  140  and the UE  160  and along which communication in further directional beams can be made between the TRP  140  and the UE  160  at a sufficiently high quality (for example by the RSRP being higher than some quality threshold value). Hence, there might be more than one path between the TRP  140  and the UE  160  that can be used for reliable communication between the TRP  140  and the UE  160 . The angular diversity between these paths  180   a : 180   d  might be represented by an angle spread value  190 . The angle spread value  190  is thus a value of the angle spread of the paths between the TRP  140  and the UE  160  that can be used for reliable communication. Ways in which the angle spread could be defined and determined will be disclosed below. 
     As noted above there is a need for improved beam management. 
     In this respect, if large overhead signaling for beam management is acceptable, a comparatively large set of candidate directional beams could be tested during one beam sweep so that even a UE  160  for which the properties of the radio propagation channel are fast-moving always is covered by their best directional beam. On the other hand, if such a large overhead signalling is not acceptable, only a comparatively small set of candidate directional beams could be tested during one beam sweep. But the question is then which directional beams to include in the candidate set of directional beams so as to reduce the risk of selecting directional beams yielding poor performance or even beam failure. 
     Selecting a suitable set of candidate directional beams allows for reducing overhead signalling whilst minimizing the risk of poor selection of directional beams for communication of data and/or control signalling. But due to differences in the radio channel conditions, and/or due to movement of the communicating radio transceiver devices one single set of candidate directional beams, or one single way to select which directional beams to be included in the set of candidate directional beams, is not likely optimal for every situation. For instance, directional beams with low angular distance between neighboring beams might yield the best set of candidate directional beams to test for a user equipment  160  at a first location (e.g. in line of sight (LoS) conditions), whilst directional beams with high angular distance between neighboring beams might yield the best set of candidate directional beams to test as the user equipment moves to a second location (e.g. in non-line of sight (NLoS) conditions where other drastically different signal paths may be important to find). 
     To further illustrate this,  FIG.  2    at (i)-(viii) shows the cumulative distribution functions (CDFs) of measurements of the resulting reference signal received power (RSRP) losses versus the best of all beams in the GoB for eight different candidate set of directional beams. In  FIG.  2 ( a )  is shown results (i)-(iii) for three candidate sets of directional beams having comparatively high spread among the beams and in  FIG.  2 ( b )  is shown results (iv)-(viii) for five candidate sets of beams having comparatively low spread among the beams. The CDFs in  FIG.  2 ( b )  all starts at comparatively high values (all above 85%) but have heavy tails (i.e., all have moderate to low slopes) whereas the CDFs in  FIG.  2 ( a )  have lower initial values, but do not suffer from the heavy tails as for the results of the candidate sets of beams in  FIG.  2 ( a ) . In this respect, a candidate set of beams having beams with comparatively low spread among the beams (such as in a neighbor sweep scheme) works well most of the time when beam jumps are sufficiently small, but such a candidate set of beams cannot be used to identify large beam jumps, which are sometimes required. In this respect, a beam jump generally refers to the angle difference in the GoB between a previous best beam and a new best beam. This causes the heavy tails shown in  FIG.  2 ( b ) . A candidate set of beams having beams with comparatively high spread among the beams works well for large beam jumps, but requires more time to find the optimal beam when only small beam jumps are needed. 
     The embodiments disclosed herein relate to mechanisms for beam management. In order to obtain such mechanisms there is provided a radio transceiver device  200   a , a method performed by the radio transceiver device  200   a , a computer program product comprising code, for example in the form of a computer program, that when run on a radio transceiver device  200   a , causes the radio transceiver device  200   a  to perform the method. 
       FIG.  3    is a flowchart illustrating embodiments of methods for beam management. The methods are performed by the radio transceiver device  200   a . The methods are advantageously provided as computer programs  920 . As disclosed above, in a first example, radio transceiver device  200   a  is part of a radio access network node  150 , and the second radio transceiver device  200   b  is part of a user equipment  160 . However, in another example, the radio transceiver device  200   a  is part of a user equipment  160 , and the second radio transceiver device  200   b  is part of a radio access network node  150 . In still another example, the radio transceiver device  200   a  is part of a first user equipment  160 , and the second radio transceiver device  200   b  is part of a second user equipment  160 . 
     It is assumed that radio transceiver device  200   a  is to perform a beam management procedure with radio transceiver device  200   b . The beam management procedure involves the radio transceiver device  200   a  to transmit (to radio transceiver device  200   b ) or receive (from radio transceiver device  200   b ) reference signals in a candidate set of directional beams. According to the herein disclosed embodiments, a selection is made of which directional beams to include in the candidate set of directional beams at a particular time. This selection is based on an angle spread value  190 . Hence, the radio transceiver device  200   a  is configured to perform steps S 102 , S 104 : 
     S 102 : The radio transceiver device  200   a  obtains an angle spread value  190  for signal paths towards a second radio transceiver device  200   b.    
     S 104 : The radio transceiver device  200   a  performs a beam management procedure for selecting which directional beam to use for communication with the second radio transceiver device  200   b . The beam management procedure involves the radio transceiver device  200   a  to transmit or receive reference signals in a candidate set of directional beams. 
     Which directional beams to include in the candidate set of directional beams is dependent on the angle spread value  190 . In this respect, the angle spread value  190  determines the sparsity of the directional beams in the candidate set of directional beams. This method allows the directional beams in the candidate set of directional beams to be dynamically updated as the angle spread value  190  changes over time. 
     The radio transceiver device  200   a  is thereby enabled to switch between using different candidate set of directional beams based on evaluation of the angle spread. 
     Embodiments relating to further details of beam management as performed by the radio transceiver device  200   a  will now be disclosed. 
     There could be different ways to define the angle spread. 
     In some aspects, the angle spread is defined as in Annex A of 3GPP TS “Spatial channel model for Multiple Input Multiple Output (MIMO) simulations”, version 15.0.0. In this document, the angle spread is denoted σ AS . With N multi-paths, and where each multi-path has M sub-paths, the angle spread σ AS  is given by: 
     
       
         
           
             
               
                 
                   
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     where again σ AS  denotes the angle spread value  190 . Further, N is the total number of reported candidate beams, and P i , θ i , and ϕ i  denotes power, elevation and azimuth, respectively, of the i:th reported candidate beam, denoting the best reported beam by index i=0. 
     There could be different ways for the radio transceiver device  200   a  to obtain the angle spread value  190  in step S 102 . 
     In some aspects, it is assumed that the angle spread value  190  is obtained in step S 102  by the radio transceiver device  200   a  receiving measurement reportings from the second radio transceiver device  200   b . Embodiments related thereto will now be disclosed. 
     That is, in some aspects, the radio transceiver device  200   a  transmits reference signals and receives reportings of measurements on the transmitted reference signals from the second radio transceiver device  200   b . Particularly, according to an embodiment, the angle spread value  190  is obtained from reports of measurements performed by the second radio transceiver device  200   b  on initial reference signals as transmitted by the radio transceiver device  200   a  in an initial set of directional beams and as received by the second radio transceiver device  200   b.    
     Intermediate reference is here made to  FIG.  4   .  FIG.  4    schematically illustrates two examples where initial reference signals are transmitted by the radio transceiver device  200   a  in an initial set of directional beams  300 . The different sized ellipses in  FIG.  4 ( a )  compared to  FIG.  4 ( b )  illustrate different angle spread of the L=4 best reported initial directional beams, where the angle spread values depend on the largest diameter D 1 , D 2 , of each of the ellipses  310   a ,  310   b . The angle spread value for the example in  FIG.  4 ( a )  is thus larger than the angle spread value for the examples in  FIG.  4 ( b ) . 
     In some aspects, the initial set of reference signals are transmitted in comparatively large set of directional beams. That is, in some embodiments, the initial set of directional beams is larger than the candidate set of directional beams. 
     There could be different ways to generate the initial set of directional beams. In some aspects, the initial set of directional beams is defined by a GoB and can be utilized for a cell-wide beam sweep. That is, in some embodiments, the initial set of directional beams is defined by a cell-covering grid of beams. 
     In some aspects, the reported directional beams are weighted based on the reported quality measure, such as RSRP per beam. That is, in some embodiments, each report identifies in which at least two directional beams in the initial set of directional beams the initial reference signals were received at highest RSRP at the second radio transceiver device  200   b . The angle spread value  190  depends on which at least two directional beams in the initial set of directional beams were identified. Each of these at least two directional beams is then weighted according to its RSRP. 
     In some aspects, the transmission of the initial reference signals occurs more seldom than the beam management procedure in step S 104 . That is, in some embodiments, the initial reference signals are transmitted less frequent in time than the reference signals transmitted in the candidate set of directional beams. 
     There could be different types of initial reference signals. In some examples, the initial reference signals are CSI-RS-BM. 
     In some aspects, it is assumed that the angle spread value  190  is in step S 102  obtained by the radio transceiver device  200   a  performing measurements on reference signals transmitted by the second radio transceiver device  200   b . That is, in some embodiments, the angle spread value  190  is obtained from measurements performed by the radio transceiver device  200   a  on reference signals as transmitted by the second radio transceiver device  200   b  and as received by the radio transceiver device  200   a.    
     There could be different ways in which the angle spread value  190  determines the sparsity of the directional beams in the candidate set of directional beams. 
     In some aspects, the angle spread value  190  is compared to angle spread threshold value. A first candidate set of directional beams might be selected in case the angle spread value  190  is higher than the angle spread threshold value and second candidate set of directional beams might be selected in case the angle spread value  190  is not higher than the angle spread threshold value. When the angle spread value  190  thus has been obtained as in step S 102 , it could be compared to the angle spread threshold value. This comparison then defined a decision rule for determining which directional beams to include in the candidate set of directional beams. In some embodiments, the candidate set of directional beams thus consists of a first set of directional beams when the angle spread value  190  is higher than the angle spread threshold value, and the candidate set of directional beams otherwise consists of a second set of directional beams. The first set of directional beams has higher sparsity than the second set of directional beams. As the skilled person understands, there might be two or more such angle spread threshold values in order to enable selection between more than two candidate sets of directional beams. 
     Intermediate reference is here made to  FIG.  5   .  FIG.  5    at (a)-(d) schematically illustrates four different examples of candidate set of directional beams  320   a ,  320   b ,  320   c ,  320   d  with decreasing sparsity. That is, candidate set of directional beams  320   a  has higher sparsity than candidate set of directional beams  320   b  and so on. Further, candidate set of directional beams  320   a  has higher vertical coverage than candidate set of directional beams  320   b  since candidate set of directional beams  320   b  only consists of beams in the three center-most vertical beam directions. Still further, candidate set of directional beams  320   a  and candidate set of directional beams  320   b  have higher horizontal coverage than candidate set of directional beams  320   c  and  320   d  since candidate set of directional beams  320   c  only consists of beams in the five, and three, center-most horizontal beam directions, respectively. Selecting between these four candidate sets of directional beams  320   a : 320   d  requires the use of three threshold values (assuming that each candidate set of directional beams is available for selection each time a new candidate set of directional beams is to be selected). Each candidate set of directional beams  320   a : 320   d  corresponds to its own angle spread value, or range of angel spread values, and for illustrative purposes it is assumed that the previously used best directional beam is located as center-most as possible among all available directional beams. The previously used best directional beam might either be included in the candidate set of directional beams or not; in the illustrative example of  FIG.  5   , the previously used best directional beam is included in the candidate sets of directional beams  320   c ,  320   d.    
     There could be different definitions of the sparsity. In some aspects, the sparsity is defined in the spatial domain whereas in other aspects the sparsity is defined in the time domain. In particular, in some embodiments, the sparsity defines the angular distance between neighbouring beams in the candidate set of directional beams. In some embodiments, the sparsity defines at which time interval the reference signals are to be transmitted or received in the candidate set of directional beams. In some embodiments, the sparsity defines a combination of the angular distance between neighbouring beams in the candidate set of directional beams and at which time interval the reference signals are to be transmitted or received in the candidate set of directional beams. 
     In some aspects, the beam management procedure is repeated using the same candidate set of directional beams until a new value of the angle spread value is obtained. That is, in some embodiments, the beam management procedure is repeated using the candidate set of directional beams as dependent on the angle spread value  190  at least until a new angle spread value  190  is obtained. In this respect, the beam management procedure is necessarily not repeated with the exact same directional beams, but all candidate sets of directional beams are dependent on the same obtained angle spread value  190  such that all candidate sets of directional beams have the same sparsity. The angle spread value  190  thus still determines the sparsity of the directional beams in all the candidate set of directional beams. 
     In further aspects, the angle spread value  190  might affect how often the beam management procedure itself is performed. That is, in some embodiments, how often in time to repeat the beam management procedure using the candidate set of directional beams as dependent on the angle spread value  190  depends on the angle spread value  190 . 
     In further aspects, the angle spread value  190  might affect the time to obtain a new angle spread value. That is, in some embodiments, the angle spread value  190  defines a recent-most angle spread value  190 , and time duration until a new angle spread value  190  is obtained depends at least on the recent-most obtained angle spread value  190 . Hence, in this respect, the time duration might be based on two or more previously obtained angle spread values  190  and this a history of previously obtained angle spread values  190  might be used to determine the time duration until a new angle spread value  190  is to be obtained. This, for example, enables the time duration until a new angle spread value is obtained to be decreased in a radio environment with highly fluctuating radio channel conditions, or vice versa, and thus to be dependent on the radio environment. 
     There could be different ways to determine which directional beams to be included in the candidate set of directional beams. 
     In some aspects, the candidate set of directional beams is based on adapting a default set of directional beams according to the angle spread value  190 . In particular, in some embodiments, the sparsity of the directional beams in the candidate set of directional beams is determined by scaling the angular distance between neighbouring beams in a default set of directional beams according to a scaling value, where the scaling value is dependent on the angle spread value  190 . For example, the directional beams in the candidate set of directional beams could be selected from a GoB with an angular distance between neighbouring beams determined according to a beam index distance (ΔBI) defined as: 
       Δ BI=±k·σ   AS   /ΔGoB.  
 
     Here, ΔGoB is the beam separation angle between neighbouring beams in the GoB, σ AS  denotes the angle spread value  190 , and k is a control parameter. The beam separation in the GoB can vary and the angle spread value  190  can also be mapped to the closest beam in the GoB taking different angle separation into account. 
     Separate values of the angle spread could be obtained for the vertical domain and the horizontal domain, respectively. Therefore, in some embodiment, the sparsity of the directional beams in the candidate set of directional beams is determined separately in vertical domain and in horizontal domain. The beam management procedure might thereby be individually controlled in each of the vertical domain and the horizontal domain. In this respect, in some scenarios where the vertical movement of the second radio transceiver devices  200   b  is smaller than their horizontal movement, the vertical angle spread value might be smaller than the horizontal angle spread value. Also, in areas with high-rise buildings, the vertical mobility of individual second radio transceiver devices  200   b  might be smaller than the horizontal mobility and the possible reflections in elevation is less likely than in azimuth. This might result in a candidate set of directional beams where the vertical angle spread value is smaller than the horizontal angle spread value. 
     Intermediate reference is now made to  FIG.  6   .  FIG.  6    schematically illustrates beam management procedures performed along a timeline. At  340  is illustrated, by means of a series of arrows, the transmission occasions of the above disclosed initial reference signals. At  300  is illustrated the initial set of directional beams in which the initial reference signals are transmitted. Also is illustrated the angle spread of the L=4 best reported initial directional beams and their corresponding ellipses. At  330  is illustrated the reporting of the initial directional beams and how angle spread of the best reported initial directional beams relates to a threshold value T. At  350  is illustrated, by means of a series of arrows, the occasions where the beam management procedure is performed. At  360  is illustrated whether the beam management procedures that are performed until a new set of initial reference signals is transmitted are to use candidate set of directional beams with low sparsity (such as any of candidate set of directional beams  320   c  or  320   d ) or candidate set of directional beams with high sparsity (such as any of candidate set of directional beams  320   a  or  320   b ). 
     In some aspects, when the beam management procedure involves transmitting the reference signals, the second radio transceiver device  200   b  performs measurements on the transmitted reference signals and reports back the measurements to the radio transceiver device  200   a . That is, according to this embodiment, the radio transceiver device  200   a  is configured to perform (optional) step S 106 : 
     S 106 : The radio transceiver device  200   a  receives reports of measurements performed by the second radio transceiver device  200   b  on the reference signals having been transmitted by the radio transceiver device  200   a  in the candidate set of directional beams. 
     The selected directional beam is then utilized for further communication, for example in terms of data signalling or control signalling, with the second radio transceiver device  200   b . That is, according to this embodiment, the radio transceiver device  200   a  is configured to perform (optional) step S 108 : 
     S 108 : The radio transceiver device  200   a  communicates with the second radio transceiver device  200   b  using the selected directional beam in the candidate set of directional beams as indicated in the reports. 
     The radio transceiver device  200   b  in the user equipment  160  may have beamforming and a large set of beam candidates. To search for the best beam among these beams is also a trade-off between loss compared to best beam, time to find best beam and cost in sending reference signals and measuring. The methods described above can thus similarly be applied to select beam scanning both in time and in angular sparsity. This applies both for communication with a transmission and reception point  140  (i.e., when radio transceiver device  200   a  is part of the transmission and reception point  140 ) or another UE  160  (i.e., when radio transceiver device  200   a  is part of another user equipment  160 ). 
     For example, an angle spread value can be obtained by the radio transceiver device  200   b  in the user equipment  160  by measuring signal strength on received beams, such as measuring on DMRS in SSB or data transmissions. The scanning for best received beam among candidate beams is then adapted to angle spread according to any of the above described methods, with sparser search for large angle spread than for narrow angle spread. 
       FIG.  7    schematically illustrates, in terms of a number of functional units, the components of a radio transceiver device  200   a ,  200   b  according to an embodiment. Processing circuitry  210  is 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 product  910  (as in  FIG.  9   ), e.g. in the form of a storage medium  230 . The processing circuitry  210  may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA). 
     Particularly, the processing circuitry  210  is configured to cause the radio transceiver device  200   a ,  200   b  to perform a set of operations, or steps, as disclosed above. For example, the storage medium  230  may store the set of operations, and the processing circuitry  210  may be configured to retrieve the set of operations from the storage medium  230  to cause the radio transceiver device  200   a ,  200   b  to perform the set of operations. The set of operations may be provided as a set of executable instructions. 
     Thus the processing circuitry  210  is thereby arranged to execute methods as herein disclosed. The storage medium  230  may 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 radio transceiver device  200   a ,  200   b  may further comprise a communications interface  220  at least configured for communications with other entities, functions, nodes, and devices of the communication network  100 , such as another radio transceiver device  200   a ,  200   b ,  200   b . As such the communications interface  220  may comprise one or more transmitters and receivers, comprising analogue and digital components. The processing circuitry  210  controls the general operation of the radio transceiver device  200   a ,  200   b  e.g. by sending data and control signals to the communications interface  220  and the storage medium  230 , by receiving data and reports from the communications interface  220 , and by retrieving data and instructions from the storage medium  230 . Other components, as well as the related functionality, of the radio transceiver device  200   a ,  200   b  are omitted in order not to obscure the concepts presented herein. 
       FIG.  8    schematically illustrates, in terms of a number of functional modules, the components of a radio transceiver device  200   a ,  200   b  according to an embodiment. 
     The radio transceiver device  200   a ,  200   b  of  FIG.  8    comprises a number of functional modules; an obtain module  210   a  configured to perform step S 102 , and a beam management module  210   b  configured to perform step S 104 . The radio transceiver device  200   a ,  200   b  of  FIG.  8    may further comprise a number of optional functional modules, such as any of a receive module  210   c  configured to perform step S 106 , and a communicate module  210   d  configured to perform step S 108 . In general terms, each functional module  210   a - 210   d  may 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 medium  230  which when run on the processing circuitry makes the radio transceiver device  200   a ,  200   b  perform the corresponding steps mentioned above in conjunction with  FIG.  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 modules  210   a - 210   d  may be implemented by the processing circuitry  210 , possibly in cooperation with the communications interface  220  and/or the storage medium  230 . The processing circuitry  210  may thus be configured to from the storage medium  230  fetch instructions as provided by a functional module  210   a - 210   d  and to execute these instructions, thereby performing any steps as disclosed herein. 
     The radio transceiver device  200   a ,  200   b  may be provided as a standalone device or as a part of at least one further device. For example, the radio transceiver device  200   a ,  200   b  may be provided in a node of the radio access network  110 , such as in a radio access network node  150 , or in a node of the core network  120 , or in a UE  160 . Alternatively, functionality of the radio transceiver device  200   a ,  200   b  may 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 radio transceiver device  200   a ,  200   b  may be executed in a first device, and a second portion of the of the instructions performed by the radio transceiver device  200   a ,  200   b  may 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 radio transceiver device  200   a ,  200   b  may be executed. Hence, the methods according to the herein disclosed embodiments are suitable to be performed by a radio transceiver device  200   a ,  200   b  residing in a cloud computational environment. Therefore, although a single processing circuitry  210  is illustrated in  FIG.  7    the processing circuitry  210  may be distributed among a plurality of devices, or nodes. The same applies to the functional modules  210   a - 210   d  of  FIG.  8    and the computer program  920  of  FIG.  9   . 
       FIG.  9    shows one example of a computer program product  910  comprising computer readable storage medium  930 . On this computer readable storage medium  930 , a computer program  920  can be stored, which computer program  920  can cause the processing circuitry  210  and thereto operatively coupled entities and devices, such as the communications interface  220  and the storage medium  230 , to execute methods according to embodiments described herein. The computer program  920  and/or computer program product  910  may thus provide means for performing any steps as herein disclosed. 
     In the example of  FIG.  9   , the computer program product  910  is 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 product  910  could 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 program  920  is here schematically shown as a track on the depicted optical disk, the computer program  920  can be stored in any way which is suitable for the computer program product  910 . 
       FIG.  10    is a schematic diagram illustrating a telecommunication network connected via an intermediate network  420  to a host computer  430  in accordance with some embodiments. In accordance with an embodiment, a communication system includes telecommunication network  410 , such as a 3GPP-type cellular network, which comprises access network  411 , such as radio access network  110  in  FIG.  1   , and core network  414 , such as core network  120  in  FIG.  1   . Access network  411  comprises a plurality of radio access network nodes  412   a ,  412   b ,  412   c , such as NBs, eNBs, gNBs (each corresponding to the radio access network node  150  of  FIG.  1   ) or other types of wireless access points, each defining a corresponding coverage area, or cell,  413   a ,  413   b ,  413   c . Each radio access network nodes  412   a ,  412   b ,  412   c  is connectable to core network  414  over a wired or wireless connection  415 . A first UE  491  located in coverage area  413   c  is configured to wirelessly connect to, or be paged by, the corresponding network node  412   c . A second UE  492  in coverage area  413   a  is wirelessly connectable to the corresponding network node  412   a . While a plurality of UE  491 ,  492  are 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 node  412 . The UEs  491 ,  492  correspond to the UE  160  of  FIG.  1   . 
     Telecommunication network  410  is itself connected to host computer  430 , 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 computer  430  may 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. Connections  421  and  422  between telecommunication network  410  and host computer  430  may extend directly from core network  414  to host computer  430  or may go via an optional intermediate network  420 . Intermediate network  420  may be one of, or a combination of more than one of, a public, private or hosted network; intermediate network  420 , if any, may be a backbone network or the Internet; in particular, intermediate network  420  may comprise two or more sub-networks (not shown). 
     The communication system of  FIG.  10    as a whole enables connectivity between the connected UEs  491 ,  492  and host computer  430 . The connectivity may be described as an over-the-top (OTT) connection  450 . Host computer  430  and the connected UEs  491 ,  492  are configured to communicate data and/or signaling via OTT connection  450 , using access network  411 , core network  414 , any intermediate network  420  and possible further infrastructure (not shown) as intermediaries. OTT connection  450  may be transparent in the sense that the participating communication devices through which OTT connection  450  passes are unaware of routing of uplink and downlink communications. For example, network node  412  may not or need not be informed about the past routing of an incoming downlink communication with data originating from host computer  430  to be forwarded (e.g., handed over) to a connected UE  491 . Similarly, network node  412  need not be aware of the future routing of an outgoing uplink communication originating from the UE  491  towards the host computer  430 . 
       FIG.  11    is a schematic diagram illustrating host computer communicating via a radio access network node with a UE over a partially wireless connection in accordance with some embodiments. Example implementations, in accordance with an embodiment, of the UE, radio access network node and host computer discussed in the preceding paragraphs will now be described with reference to  FIG.  11   . In communication system  500 , host computer  510  comprises hardware  515  including communication interface  516  configured to set up and maintain a wired or wireless connection with an interface of a different communication device of communication system  500 . Host computer  510  further comprises processing circuitry  518 , which may have storage and/or processing capabilities. In particular, processing circuitry  518  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. Host computer  510  further comprises software  511 , which is stored in or accessible by host computer  510  and executable by processing circuitry  518 . Software  511  includes host application  512 . Host application  512  may be operable to provide a service to a remote user, such as UE  530  connecting via OTT connection  550  terminating at UE  530  and host computer  510 . The UE  530  corresponds to the UE  160  of  FIG.  1   . In providing the service to the remote user, host application  512  may provide user data which is transmitted using OTT connection  550 . 
     Communication system  500  further includes radio access network node  520  provided in a telecommunication system and comprising hardware  525  enabling it to communicate with host computer  510  and with UE  530 . The radio access network node  520  corresponds to the radio access network node  150  of  FIG.  1   . Hardware  525  may include communication interface  526  for setting up and maintaining a wired or wireless connection with an interface of a different communication device of communication system  500 , as well as radio interface  527  for setting up and maintaining at least wireless connection  570  with UE  530  located in a coverage area (not shown in  FIG.  11   ) served by radio access network node  520 . Communication interface  526  may be configured to facilitate connection  560  to host computer  510 . Connection  560  may be direct or it may pass through a core network (not shown in  FIG.  11   ) of the telecommunication system and/or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, hardware  525  of radio access network node  520  further includes processing circuitry  528 , 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 node  520  further has software  521  stored internally or accessible via an external connection. 
     Communication system  500  further includes UE  530  already referred to. Its hardware  535  may include radio interface  537  configured to set up and maintain wireless connection  570  with a radio access network node serving a coverage area in which UE  530  is currently located. Hardware  535  of UE  530  further includes processing circuitry  538 , 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. UE  530  further comprises software  531 , which is stored in or accessible by UE  530  and executable by processing circuitry  538 . Software  531  includes client application  532 . Client application  532  may be operable to provide a service to a human or non-human user via UE  530 , with the support of host computer  510 . In host computer  510 , an executing host application  512  may communicate with the executing client application  532  via OTT connection  550  terminating at UE  530  and host computer  510 . In providing the service to the user, client application  532  may receive request data from host application  512  and provide user data in response to the request data. OTT connection  550  may transfer both the request data and the user data. Client application  532  may interact with the user to generate the user data that it provides. 
     It is noted that host computer  510 , radio access network node  520  and UE  530  illustrated in  FIG.  11    may be similar or identical to host computer  430 , one of network nodes  412   a ,  412   b ,  412   c  and one of UEs  491 ,  492  of  FIG.  10   , respectively. This is to say, the inner workings of these entities may be as shown in  FIG.  11    and independently, the surrounding network topology may be that of  FIG.  10   . 
     In  FIG.  11   , OTT connection  550  has been drawn abstractly to illustrate the communication between host computer  510  and UE  530  via network node  520 , without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from UE  530  or from the service provider operating host computer  510 , or both. While OTT connection  550  is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network). 
     Wireless connection  570  between UE  530  and radio access network node  520  is 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 UE  530  using OTT connection  550 , in which wireless connection  570  forms 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. 
     A measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring OTT connection  550  between host computer  510  and UE  530 , in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring OTT connection  550  may be implemented in software  511  and hardware  515  of host computer  510  or in software  531  and hardware  535  of UE  530 , or both. In embodiments, sensors (not shown) may be deployed in or in association with communication devices through which OTT connection  550  passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software  511 ,  531  may compute or estimate the monitored quantities. The reconfiguring of OTT connection  550  may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect network node  520 , and it may be unknown or imperceptible to radio access network node  520 . Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling facilitating host computer&#39;s  510  measurements of throughput, propagation times, latency and the like. The measurements may be implemented in that software  511  and  531  causes messages to be transmitted, in particular empty or ‘dummy’ messages, using OTT connection  550  while it monitors propagation times, errors etc. 
     The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.