Method for determining a beam for a downlink signal or a downlink channel

Abstract

The invention refers to a method for beam determination. The method comprises transmitting (102a), by the base station (20), a configuration to the UE (10), the configuration comprising a definition of uplink reference signal resources, also referred to as UL-RS resources; transmitting (104a), by the UE (10) an uplink reference signal to the base station (20) on at least one beam using the UL-RS resources that are defined in the received configuration, wherein the uplink reference signal is received by the base station (20) from the UE (10) by using some or all of the uplink reference signal resources that are defined in the transmitted configuration; determining (105a), by the base station (20), one or more preferred beams of the at least one beam based on the received uplink reference signal of each received beam and transmitting (105) a reference signal indication to the UE (10), wherein the reference signal indication is indicating at least one UL-RS resource on which the uplink reference signal has been transmitted by the UE (10) on one of the preferred one or more beams; transmitting (106a), by the base station (20), a downlink signal and / or a downlink channel to the UE (10); and receiving (106b), by the UE (10), the downlink signal and / or the down- link channel using a beam that is based on the beam that has been used for transmitting the uplink reference signal on the UL-RS resource that is indicated in the reference signal indication.

Description

[0001] Method for determining a beam for a downlink signal or a downlink channel

[0002] Technical field

[0003] The invention refers to a method for determining a beam for a downlink signal or a downlink channel.

[0004] Background

[0005] In modern communication networks, beamforming can be used for optimizing the use of available communication resources. Beamforming allows a member of the communication network, for example a base station or a user equipment, to send radio beams in specific spatial directions. It is a challenge to determine a pair of optimal beams for sending and receiving information when establishing or maintaining a communication between two members of the communication network without unnecessarily increasing a necessary management information.

[0006] A method for a User Equipment (UE) according to the disclosure comprises receiving a configuration transmitted by a base station, the configuration comprising a definition of uplink reference signal resources (UL-RS resources), transmitting an uplink reference signal to the base station on at least one beam using the UL-RS resources that are defined in the received configuration, receiving a reference signal indication transmitted by the base station, wherein the reference signal indication is indicating at least one UL-RS resource that has been used for transmitting the uplink reference signal; and receiving a downlink signal and / or a downlink channel using a beam that is based on the beam that has been used for transmitting the uplink reference signal on the UL-RS resource that is indicated in the reference signal indication.

[0007] A user equipment (UE) according to the disclosure comprises a processing circuitry, a memory and a transceiver, wherein said memory contains instructions, which when executed by said processing circuitry causes the UE to perform the method according to the disclosure, in particular to receive a configuration transmitted by a base station, the configuration comprising a definition of uplink reference signal resources, also referred to as UL-RS resources; transmit an uplink reference signal to the base station on at least one beam using the UL-RS resources that are defined in the received configuration; receive a reference signal indication transmitted by the base station, wherein the reference signal indication is indicating at least one UL-RS resource that has been used for transmitting the uplink reference signal; and receive a downlink signal and / or a downlink channel using a beam that is based on the beam that has been used for transmitting the uplink reference signal on the UL-RS resource that is indicated in the reference signal indication. The method comprises receiving a configuration transmitted by the base station, wherein the configuration comprises a definition of the UL-RS resources. The UL-RS resources are resources in time and / or frequency domain of a transmission band and / or a code domain that is used for the communication between the UE and the base station. The code domain preferably defines a type of coding that is applied to the reference signal. The definition of the UL-RS resources preferably comprises a definition of a set or multiple sets of UL-RS resources. UL-RS resources are resources that are foreseen to be used for a transmission of an uplink reference signal. An uplink reference signal is a reference signal that is transmitted from the UE to the base station that allows the base station to determine characteristics of the transmission channel that has been used for transmitting the reference signal. The UL-RS resources are used by the UE for transmitting the uplink reference signal. The base station is assigning the UL-RS resources to the UE and is therefore capable to receive the uplink reference signal on the UL-RS resources. Preferably, the UL- RS resources define a time and / or frequency within a predefined transmission interval and band, for example in a resource unit (RU).

[0008] The reference signal is preferably a 5G or 6G reference signal. Exemplary reference signals for 5G are the demodulation reference signal (DMRS), the phase tracking reference signal (PTRS) and the sounding reference signal (SRS). The base station is preferably an evolved Node B (eNodeB), a next generation Node B (gNodeB) or a base station for a 6G network.

[0009] The method comprises transmitting the uplink reference signal to the base station on at least one beam using some or all of the UL-RS resources that are defined in the configuration that is received by the UE from the base station. Preferably, that the same type of reference signal is transmitted on different beams. On each beam of the multiple beams the reference signal is transmitted at least once. Preferably, the reference signal is transmitted exactly once per beam. In the alternative, the reference signal is transmitted multiple times per beam, using different UL-RS resources. For each beam, some or all of the UL-RS resources that are defined in the configuration that is received by the UE are used for transmitting the reference signal. Preferably, different UL-RS resources are used in each beam of the multiple beams. The uplink reference signal is transmitted to the base station on at least one beam. The uplink reference signal can be transmitted on a single beam. In this case the method allows to determine whether this beam is suitable for receiving the downlink signal and / or the downlink channel. The uplink reference signal can also be transmitted to the base station on multiple beams. In this case the method allows to determine one or more beams that are most suitable for receiving the downlink signal and / or the downlink channel.

[0010] The method comprises receiving the reference signal indication transmitted by base station by the UE, wherein the reference signal indication is indicating at least one UL-RS resource that has been used for transmitting the uplink reference signal. With the reception of the uplink reference signal on one or multiple beams, the base station is capable to identify one or more specific beams of the at least one beam based on the quality of the received reference signals, which are received by the base station and have been transmitted by the UE via these beams, wherein a preferable or multiple preferable beams are identified. The preferable or multiple preferable beams are indicated to the UE by the base station with the reference signal indication. The UE is preferably determining which beam has been used for transmitting the reference signal on the UL-RS resource that is indicated in the reference signal indication for determining the beams that are to be used for receiving the one or more downlink signals and / or a downlink channel.

[0011] The reference signal indication is done by pointing to one or more of the UL-RS resources. As the UE is aware of the UL-RS resources that have been used for transmitting the reference signal, the UE is able to determine the beam that should be used for receiving the downlink signal and / or the downlink channel.

[0012] The UE is receiving the downlink signal and / or the downlink channel using a beam that is based on the beam that has been used for transmitting the reference signal on the UL-RS resource that is indicated in the reference signal indication. The UE is using a beam that is based on the beam that has been used for transmitting the reference signal, which includes that the UE is determining another beam based on the beam that has been used for transmitting the reference signal. Accordingly, the UE is expecting to receive information on the beam that has been indicated via the reference signal indication, wherein the information is a dataset that is communicated from the base station to the UE via the downlink signal and / or the downlink channel. In particular, the receiving of the downlink signal and / or the downlink channel comprises a configuration of a transceiver of the UE for receiving the downlink signal and / or a downlink channel on the beams that have been indicated via the reference signal indication. Optionally, the UE is configured for receiving the downlink signal and / or the downlink channel from the base station using only the one or more beams that have been indicated via the reference signal indication.

[0013] Accordingly, the UE is configured for receiving the downlink signal and / or the downlink channel on a beam that is determined based on an uplink reference signal. It is not necessary that the base station is transmitting a downlink reference signal. Also, it is not necessarily that the base station is transmitting a dedicated identifier of a beam for indicating the beams that will be used for transmitting the downlink signal and / or the downlink channel. Rather than that, a UL-RS resource is indicated and the UE will determine the beam from information that defines a relation between the UL-RS resources and corresponding beams that have been used for transmitting the reference signal on these UL-RS resources.

[0014] In NR it is currently not possible to use an UL-RS (e.g., SRS) as beam indication for downlink channels / signals. However, in case of AI / ML-based solution based on UL-RS, it is beneficial when an uplink reference signal index is used as beam indication also for DL signals / channels, as it is one reason why UL-RS based beam management is preferred for AI / ML (artificial I ntell igence / machi ne learning) based beam prediction that then the network can do the AI / ML based predictions instead of the UE, which usually leads to better performance since the network node can train the beam prediction model on the specific scenario where it is used.

[0015] The described techniques allow a base station to perform DL beam indication and hence use a beam pair link for DL channels / signals based on UL beam management, which will reduce overhead signalling and latency for deployments with AI / ML based beam management using UL beam management. The dependent claims define preferable embodiments.

[0016] In particular, the uplink reference signal is transmitted to the base station on multiple beams using the UL-RS resources that are defined in the received configuration. In particular, the uplink reference signal is transmitted to the base station on multiple beams using the UL-RS resources, wherein a different UL-RS resource is used on each beam or wherein different UL-RS resources are used on each beam. Preferably, each one of the multiple beams has an individual UL-RS resource assigned that is different from the UL-RS resource of the other beams of the multiple beams. This allows a determination of a beam from multiple possible beams and allows a distinct identification of the preferable beams.

[0017] In particular , the method comprises receiving a trigger from the base station to transmit the uplink reference signal, wherein the uplink reference signal is transmitted to the base station on the at least one beam in reaction to receiving the trigger. This is advantageous, as this allows the base station to synchronize a time in which the base station is listening for a reception of the uplink reference signal with a time at which the UE is transmitting the uplink reference signal to the base station on the multiple beams using some or all of the UL-RS resources.

[0018] In particular , the method comprises transmitting a support indication to the base station, wherein the support indication is indicating that the UE is capable to determine a beam for receiving the downlink signal and / or the downlink channel based on the uplink reference signal. With transmitting the support indication, the base station is made aware that the UE can be configured to select the beams for receiving the downlink signal and / or the downlink channel without receiving a downlink reference signal from the base station. Based on the support indication, the base station can determine whether a downlink reference signal is to be transmitted to the UE or not.

[0019] In particular, the support indication is indicating a support of the UE of DCI (Downlink Control Information) based beam indication for the downlink signal and / or the downlink channel based on the uplink reference signal, MAC-CE (Medium Access Control-Control Element) based beam indication for the downlink signal and / or the downlink channel based on the uplink reference signal, RRC (Radio Resource Control) based beam indication for the downlink signal and / or the downlink channel based on the uplink reference signal and / or a number of simultaneous beam indications for the downlink signal and / or the downlink channel based on the uplink reference signal. A DCI based beam indication is a beam indication in which the base station is indicating the UL-RS resources via DCI. A MAC-CE based beam indication is a beam indication in which the base station is indicating the UL-RS resources via a MAC-CE. A RRC based beam indication is a beam indication in which the base station is indicating the UL-RS resources via RRC. A support of a number of simultaneous beam indications for the downlink signal and / or the downlink channel based on the uplink reference signal allows an indication of multiple beams within a single message that is transmitted to the UE by pointing to multiple UL-RS resources. In particular, the reference signal indication is pointing to one or more of the UL-RS resources, preferably using a global uplink reference signal resource set ID and a global uplink reference signal resource ID, a global uplink reference signal resource set ID and a local uplink reference signal resource ID, a local uplink reference signal resource set ID and a global uplink reference signal resource ID, a local uplink reference signal resource set ID and a local uplink reference signal resource ID, only a global uplink reference signal resource ID, only a semi-local uplink reference signal resource ID, or only a local uplink reference signal resource ID. A global ID is an ID that is unique per serving cell, per serving cell group or per band width part (BWP). A local ID is an ID that defines a position of an UL- RS resource in an indicated UL-RS resource set. An uplink reference signal resource ID is an identifier that is pointing to a reference signal resource, wherein the reference signal resource can be defined in one of multiple UL-RS resource sets. An uplink reference signal resource set ID is an identifier that is pointing to a UL-RS resource set. A global uplink reference signal resource set ID is a global ID and is preferably an index that is pointing at one UL-RS resource set. A global uplink reference signal resource ID is a global ID and is preferably an index that is pointing to an UL-RS resource from one or multiple different UL-RS resource sets. A local uplink reference signal resource ID is a local ID and is preferably an index that is pointing at one UL-RS resource set. The local uplink reference signal resource ID can for example be used in case different UL-RS resources are configured in different UL-RS resource sets. A local uplink reference signal resource set ID is a local ID and is preferably an index that is pointing to an UL-RS resource from one or multiple different UL-RS resource sets. Performing a beam indication by pointing to one or more of the UL-RS resources allows to indicate a beam without having knowledge of any designated beam indicator, as the UE is aware of the UL-RS resources that have been used on the individual beams of the multiple beams.

[0020] In particular, the reference signal indication is conveyed in a downlink joint TCI state (Joint / DL TCI state), wherein the UL-RS resources are configured as QCL-Type D / spatial relation in the DL / Joint TCI state. The Joint / DL TCI state is set on the UE based on the reference signal indication. The downlink joint TCI state is a status that is set on the UE to define a relation between different resources that are used for transmitting and receiving signals, wherein it is defined with the downlink joint TCI state that an uplink resource, here an UL-RS resource that has been used for transmitting the reference signal, has a common characteristic with a downlink resource that will be used for receiving the downlink signal and / or a downlink channel. The QCL-Type D / spatial relation defines that the common characteristic is a spatial characteristic, which defines the beam that has been used for transmitting the reference signal. Therefore, by setting the downlink joint TCI state for the UE, it is defined that the same beam that has been used for transmitting the reference signal that is indicated in reference signal indication is to be used for receiving the downlink signal and / or a downlink channel. A link between the spatial alignment of the beam that is used for transmitting the reference signal and the beam that is used for receiving the downlink signal and / or the downlink channel is established.

[0021] In particular, the reference signal indication is conveyed in one or more fields in a Downlink Control Information, DCI, wherein the reference signal indication is preferably performed by using an indicator that is pointing towards one of the UL-RS resources. Therefore, the process for transmitting DCI information from the base station to the UE can be used for transmitting the reference signal indication. In particular, the one or more fields in DCI for conveying the reference signal indication are included in the DCI based on a Radio Resource Control, RRC, configuration. That is, it is defined in the RRC configuration whether a DCI comprises the field for reference signal indication or not. Therefore, it can be avoided that unnecessary information is transmitted.

[0022] In particular, two or more UL-RS resources are indicated in one field in the DCI. This allows the UE to define multiple beams that can be configured for receiving the downlink signal and / or the downlink channel.

[0023] In particular, a corresponding number of downlink joint TCI states and UL-RS resources are indicated in the one or more fields in the DCI. Preferably, one Joint / DL TCI state is assigned to each UL-RS resource. Therefore, a characteristic can be defined for each beam that is used for receiving the downlink signal and / or the downlink channel.

[0024] In particular, a QCL Type A, B and / or C is determined for the received downlink signals and / or for the downlink channel from a Joint / DL TCI state, and a spatial filter for the received downlink signal and / or downlink channel is determined based on the indicated UL-RS resource. This means that characteristics for the received downlink signal and / or for the downlink channel are determined from a Joint / DL TCI state, which is QCL Type A, B and / or C, for the received downlink signal and / or for the downlink channel. At the same time, the spatial filter for the received downlink signal and / or downlink channel is determined based on the indicated UL-RS resource. Therefore, additional characteristics of the indicated UL-RS resource can be used when receiving the downlink signal and / or the downlink channel, in addition to the spatial filter characteristics that define the beam for receiving the downlink signal and / or the downlink channel. In particular, the Joint / DL TCI state being set to QCL Type A defines that the doppler shift, doppler spread, average delay and delay speed of the indicated UL-RS resource can be applied for the downlink signal and / or for the downlink channel. The Joint / DL TCI state being set to QCL Type B defines that the doppler shift and doppler spread of the indicated UL-RS resource can be applied for the downlink signal and / or for the downlink channel. The Joint / DL TCI state being set to QCL Type C defines that the an average delay and doppler shift of the indicated UL-RS resource can be applied for the downlink signal and / or for the downlink channel.

[0025] In particular, the UE is configured with intra-band carrier aggregation with multiple serving cells, wherein the UL- RS resources are configured and transmitted in a first serving cell, wherein the reference signal indication that is pointing the at least one UL-RS resource is conveyed in the first serving cell, and wherein the determined UE beam is used for receiving the downlink signal and / or the downlink channel in the first serving cell and at least one additional serving cell.

[0026] In particular, the UE is configured via RRC with a list of serving cells, wherein the additional serving cells are defined by the list of serving cells. A method for a base station according to the disclosure comprises transmitting a configuration to a user equipment, U E, the configuration comprising a definition of uplink reference signal resources, receiving an uplink reference signal from the UE that was transmitted on at least one beam by the UE, using some or all of the uplink reference signal resources that are defined in the transmitted configuration, determining one or more preferred beams of the at least one beam based on the received uplink reference signal of each received beam, and transmitting a reference signal indication to the UE, wherein the reference signal indication is indicating at least one UL-RS resource on which the uplink reference signal has been transmitted by the UE on one of the one or more preferred beams. A base station using the method is capable to determine an indicator for beam selection in interaction with an UE according to the invention. In particular, the method for the base station comprises transmitting a downlink signal and / or a downlink channel using the beam that has been used for receiving the reference signal on the UL-RS resource that is indicated in the reference signal indication. In particular, the uplink reference signal is received on multiple beams. In particular, one or more preferred beams of the multiple beams are determined based on the received uplink reference signal of each beam. In particular, the uplink reference signal is used for determining the one or more preferred beams. In particular, the base station is transmitting a trigger to the UE, wherein the trigger is for triggering a transmission of the uplink reference signal on at least one beam by the UE. In particular, the base station is receiving a support indication that was transmitted by the UE, wherein the support indication is indicating that the UE is capable to determine a beam for receiving the downlink signal and / or the downlink channel based on the uplink reference signal, and is performing the determining of one or more preferred beams of the at least one beam and transmitting the reference signal indication to the UE if the support indication was received.

[0027] A base station according to the disclosure comprises a processing circuitry, a memory and a transceiver, wherein said memory contains instructions, which when executed by said processing circuitry causes the base station to transmit a configuration to a user equipment, UE, the configuration comprising a definition of uplink reference signal resources; receive an uplink reference signal from the UE that was transmitted on at least one beam by the UE, using some or all of the uplink reference signal resources that are defined in the transmitted configuration; determine one or more preferred beams of the at least one beam based on the received uplink reference signal of each received beam; and transmit a reference signal indication to the UE, wherein the reference signal indication is indicating at least one UL-RS resource on which the uplink reference signal has been transmitted by the UE on one of the one or more preferred beams. Such base station is capable to determine an indicator for beam selection in interaction with an UE according to the invention. Preferably, said memory contains instructions, which when executed by said processing circuitry causes the base station to transmit a downlink signal and / or a downlink channel using the beam that has been used for receiving the reference signal on the UL-RS resource that is indicated in the reference signal indication. In particular, the uplink reference signal is received on multiple beams. In particular, one or more preferred beams of the multiple beams are determined based on the received uplink reference signal of each beam. In particular, the uplink reference signal is used for determining the one or more preferred beams.

[0028] A system that comprises a base station according to the disclosure and a UE according to the disclosure is advantageous and is capable to achieve all advantages of the invention. A method for a system that comprises a User Equipment, UE, and a base station according to the disclosure comprises transmitting, by the base station, a configuration to the UE, the configuration comprising a definition of uplink reference signal resources, also referred to as UL-RS resources; transmitting, by the UE an uplink reference signal from the UE to the base station on at least one beam using the UL-RS resources that are defined in the received configuration, wherein the uplink reference signal is received by the base station from the UE by using some or all of the uplink reference signal resources that are defined in the transmitted configuration; determining, by the base station, one or more preferred beams of the at least one beam based on the received uplink reference signal of each received beam; transmitting, by the base station, a reference signal indication to the UE, wherein the reference signal indication is indicating at least one UL-RS resource on which the uplink reference signal has been transmitted by the UE on one of the preferred one or more beams; transmitting, by the base station, a downlink signal and / or a downlink channel to the UE; and receiving, by the UE, the downlink signal and / or the downlink channel using a beam that is based on the beam that has been used for transmitting the uplink reference signal on the UL-RS resource that is indicated in the reference signal indication.

[0029] A communication system according to an aspect of the disclosure includes a host computer comprising processing circuitry configured to provide user data; and a communication interface configured to forward the user data to a cellular network for transmission to a user equipment (UE), wherein the cellular network comprises a base station having a radio interface and processing circuitry, the base station's processing circuitry configured to perform the method for a base station according to the invention. The communication system preferably further includes the base station. Preferably, the communication system comprises the UE, wherein the UE is configured to communicate with the base station. Further preferably, the processing circuitry of the host computer is configured to execute a host application, thereby providing the user data; and the UE comprises processing circuitry configured to execute a client application associated with the host application. Such a communication system is efficiently using availably radio resources, allowing that any data that is to be communicated from the host computer to the UE is reliably communicated, even if the UE is in an environment with limited availability of radio resources.

[0030] A communication system according to an aspect of the disclosure includes a host computer comprising processing circuitry configured to provide user data; and a communication interface configured to forward user data to a cellular network for transmission to a user equipment (UE), wherein the UE comprises a radio interface and processing circuitry, the UE's processing circuitry configured to perform the method for a UE according to the invention. The communication system preferably further includes the UE. Preferably, the cellular network further includes a base station configured to communicate with the UE. Preferably, the processing circuitry of the host computer is configured to execute a host application, thereby providing the user data; and the UE processing circuitry is configured to execute a client application associated with the host application. Such a communication system is efficiently using availably radio resources, allowing that any data that is to be communicated from the host computer to the UE is reliably communicated, even if the UE is in an environment with limited availability of radio resources. Brief description of the drawings

[0031] Fig. 1 is illustrating details of a beam management procedure,

[0032] Fig. 2a is illustrating an example of "Joint DL / UL TCI” operation,

[0033] Fig. 2b is illustrating an example of "Separate DL / UL TCI” operation,

[0034] Fig. 3 is illustrating techniques for UL beam management,

[0035] Fig. 4 is a flowchart of a method according to the invention,

[0036] Fig. 5 is illustrating an exemplary structure of a user equipment 10 according to the invention,

[0037] Fig. 6 is illustrating an exemplary structure of base station 20 according to the invention,

[0038] Fig. 7 is illustrating an exemplary system according to the invention, and

[0039] Fig. 8 is illustrating a communication system according to the invention.

[0040] Detailed description

[0041] The methods and devices according to the invention allow a further improvements of existing communication standards in which a user equipment (UE) is communicating with a base station, such as an evolved Node B (eNodeB or eNB) or a next generation Node B (gNodeB or gNB).

[0042] In existing communication standards, it is known that reference signals are used for determining a quality of a communication channel. An exemplary reference signal (RS) is the Sounding Reference Signal (SRS).

[0043] In New Radio (NR), the SRS is used for providing Channel State Information (CSI) to the gNB in the Uplink (UL). For example, an SRS is used for deriving appropriate transmission / reception beams and / or to perform link adaptation, that is for setting a transmission rank and a Modulation and Coding Scheme (MCS). Also, the SRS can be used for selecting downlink (DL) Multiple-Input Multiple-Output (MIMO) precoding, in particular for Physical Downlink Shared Channel (PDSCH) transmissions, and can be used for selecting UL MIMO precoding, in particular for the Physical Uplink Shared Channel (PUSCH) transmissions.

[0044] In Long Term Evolution (LTE) and NR, the SRS is configured via Radio Resource Control (RRC), where parts of the configuration can be updated (for reduced latency) through Medium Access Control (MAC) - Control Element (CE) signaling. The configuration includes, for example, the SRS resource allocation, that is the physical mapping and the sequence to use, as well as a time-domain behaviour such as aperiodic, semi-persistent, or periodic. For aperiodic SRS transmission, the RRC configuration does not activate an SRS transmission from the UE but instead a dynamic activation trigger is transmitted from the gNB in the DL, via the Downlink Control Information (DCI) in the Physical Downlink Control Channel (PDCCH) which instructs the UE to transmit the SRS once, at a predetermined time.

[0045] When configuring SRS transmissions, the gNB configures a set of SRS resources and a set of SRS resource sets through an SRS-Config Information Element (SRS-Config IE), wherein each SRS resource set contains one or more SRS resources.

[0046] Each SRS resource set can be configured with a certain usage (depending on what the SRS transmission shall be used for, see 3GPP TS 38.214 for further details), by setting the RRC parameter 'usage' in SRS-Config IE to one of 'antennaSwitching', ‘codebook', ‘nonCodebook', or 'beamManagement'. a) An SRS resource set that is configured with usage 'antennaSwitching' is used for reciprocity-based downlink (DL) precoding (i.e., used to sound the channel in the UL so that the gNB can use reciprocity to set a suitable DL precoders). The UE is expected to transmit one SRS port per UE antenna port. b) An SRS resource set that is configured with usage ‘codebook' is used for codebook (CB)-based UL transmission (i.e., used to sound the different UE antennas and help the gNB to determine / signal a suitable UL precoder, transmission rank, and MCS for PUSCH transmission). There are up to two SRS resources in an SRS resource set with usage ‘codebook'. How SRS ports are mapped to UE antenna ports is, however, up to UE implementation and not known to the gNB. c) An SRS resource set that is configured with usage ‘nonCodebook' is used for Non-Codebook (NCB)-based UL transmission. Specifically, the UE transmits one SRS resource per candidate beam (suitable candidate beams are determined by the UE based on CSI-RS measurements in the DL and, hence, reciprocity needs to hold). The gNB can then, by indicating a subset of these SRS resources, determine which UL beam(s) that the UE should apply for PUSCH transmission. One UL layer will be transmitted per indicated SRS resource. Note that how the UE maps SRS ports to antenna ports is up to UE implementation and not known to the gNB. d) An SRS resource set that is configured with usage 'beamManagement' is used mainly for frequency bands above 6 GHz, that is for Frequency Range (FR) 2, to evaluate different UE beams for analog beamforming arrays. The UE transmits one SRS resource per analog beam, and the gNB will perform an RS Received Power (RSRP) measurement per transmitted SRS resource and, in this way, determine a suitable UE beam that is reported to the UE.

[0047] In existing communication standards, it is further known that a Multi-beam operation can be performed between the UE and the base station.

[0048] Multi-beam operation typically comprises a beam management procedure. In high frequency range (FR2), multiple Radio Frequency (RF) beams may be used to transmit and receive signals at a gNB and a UE. For each DL beam from a gNB, there is typically an associated best UE receive (Rx) beam for receiving signals from the DL beam. The DL beam and the associated UE Rx beam forms a beam pair. The beam pair can be identified through a so-called beam management process in NR.

[0049] A DL beam is typically identified by an associated DL reference signal (RS) transmitted in the beam, either periodically, semi-persistently, or aperiodically. The DL RS for the purpose can be a Synchronization Signal (SS) block, also referred to as Synchronization Signal Block (SSB), and Physical Broadcast Channel (PBCH) block, or a Channel State Information RS (CSI-RS). By measuring all the DL RSs, the UE can determine and report to the gNB the best DL beam to use for DL transmissions. The gNB can then transmit a burst of DL-RS in the reported best DL beam to let the UE evaluate candidate UE RX beams.

[0050] Although not explicitly stated in the NR specification, beam management has been divided into three procedures P1 , P2 and P3, which are schematically illustrated in Figure 1.

[0051] A first procedure P1 is performed by a base station 20 to find a coarse direction for a UE 10 using wide gNB transmission (TX) beams 30 for covering the whole angular sector.

[0052] The first procedure P1 is expected to utilize beams with rather large beamwidths and where the beam reference signals are transmitted periodically and are shared between all UEs of the cell. Typically reference signal to use for the first procedure P1 are periodic CSI-RS or SSB. The UE 10 then reports the N best beams to the gNB 10 and their corresponding RS Received Power (RSRP) values.

[0053] A second procedure P2 is performed by the base station 20 to refine the gNB TX beam by doing a new beam search around the coarse direction found in P1 using gNB transmission (TX) beams 31. The second procedure P2 is expected to use aperiodic / or semi-persistent CSI-RS transmitted in narrow beams around the coarse direction that has been found in the first procedure P1 .

[0054] A third procedure P3 is used by the UE 10, which uses analog beamforming, to let the UE 10 find a suitable UE RX beam. The third procedure P3 is expected to use aperiodic or semi-persistent CSI-RSs repeatedly transmitted in one narrow gNB beam. One alternative way is to let the UE 10 determine a suitable UE RX beam based on the periodic SSB transmission. Since each SSB consists of four Orthogonal Frequency Division Multiplexing (OFDM) symbols, a maximum of four UE RX beams can be evaluated during each SSB burst transmission. One benefit with using SSB instead of CSI-RS is that no extra overhead of CSI-RS transmission is needed.

[0055] Multi-beam operation typically comprises techniques for beam indication. In NR, several signals can be transmitted from different antenna ports of a same base station. These signals can have the same large-scale properties such as Doppler shift / spread, average delay spread, or average delay. These antenna ports are then said to be quasi co-located (QCL).

[0056] If the UE knows that two antenna ports are QCL with respect to a certain parameter (e.g., Doppler spread), the UE can estimate that parameter based on one of the antenna ports and apply that estimate for receiving signal on the other antenna port.

[0057] For example, there may be a QCL relation between a CSI-RS for tracking RS (TRS) and the PDSCH DMRS. When UE receives the PDSCH DMRS it can use the measurements already made on the TRS to assist the DMRS reception.

[0058] Information about what assumptions can be made regarding QCL is signalled to the UE from the network. In NR, four types of QCL relations between a transmitted source RS and transmitted target RS were defined:

[0059] Type A: {Doppler shift, Doppler spread, average delay, delay spread}

[0060] Type B: {Doppler shift, Doppler spread}

[0061] Type C: {average delay, Doppler shift}

[0062] Type D: {Spatial Rx parameter}

[0063] QCL type D was introduced in NR to facilitate beam management with analog beamforming and is known as spatial QCL. There is currently no strict definition of spatial QCL, but the understanding is that if two transmitted antenna ports are spatially QCL, the UE can use the same Rx beam to receive them. This is helpful for a UE that uses analog beamforming to receive signals, since the UE needs to adjust its RX beam in some direction prior to receiving a certain signal. If the UE knows that the signal is spatially QCL with some other signal it has received earlier, then it can safely use the same RX beam to also receive this signal.

[0064] In NR, the spatial QCL relation for a DL or UL signal / channel can be indicated to the UE by using a "beam indication”. The "beam indication” is used to help the UE to find a suitable RX beam for DL reception, and / or a suitable TX beam for UL transmission. In NR, the "beam indication” for DL is conveyed to the UE by indicating a transmission configuration indicator (TCI) state to the UE, while in UL the "beam indication” can be conveyed by indicating a DLRS or UL-RS as spatial relation (in NR Rel-15 / 16) or a TCI state (since NR Rel-17).

[0065] A new unified TCI state framework was introduced in NR Rel-17 to streamline the beam management framework specified in NR Rel-15 / 16, which was overhead and latency heavy. It is possible that large part of the unified TCI state framework introduced in Rel-17 will be used as baseline for 6G beam management. The unified TCI state framework can be RRC configured in one out two modes of operation "Joint DL / UL TCI” or "Separate DL / UL TCI”. Fig. 2a shows an example of "Joint DL / UL TCI” operation with a single beam pair link used for both DL and UL signals / channels. Fig. 2b shows an example of "Separate DL / UL TCI” operation where one beam pair link is used for DL signals / channels and where another beam pair link is used for UL signals / channels on the right side.

[0066] For "Joint DL / UL TCI” one common Joint / DL TCI state (called "DLorJoint-TCI State-r17” in the specification) is used for both DL and UL signals / channels, while for "Separate DL / UL TCI”, one common Joint / DL TCI state is used for DL channels / signals and one common UL TCI state (called UL-TCI State-r17 in the specification) is used for UL signals / channels, as schematically illustrated on the left side in Figure 2. It is expected that "Joint DL / UL TCI” will be the most common use case, but "Separate DL / UL TCI”, as schematically illustrated on the right side in Figure 2, can be useful in specific scenarios where the optimal DL beam pair link differs from optimal UL beam pair link, for example in case a UE panel associated with the best DL beam pair link is affected by P-MPR (and the UE hence need to reduce the maximum allowed output power for that UE panel).

[0067] Referring to further details of beam indication for unified TCI state framework, it is noted that a TCI state ID for the unified TCI state framework can be updated in a similar way as the TCI state ID is update for PDSCH in NR Rel- 15 / 16, using one of two alternatives: a) Two-stage: RRC signalling is used to configure a number of TCI states in PDSCH-Config, and MAC-CE is used to activate / indicate a single TCI state (that TCI state will then be applied). b) Three-stage: RRC signalling is used to configure a number of TCI states in PDSCH-Config, MAC-CE is used to activate up to 8 TCI states, and a 3-bit TCI state bitfield (consisting of up to 8 codepoints) in DCI is used to indicate one of the activated TCI states (the indicated TCI state will be applied).

[0068] For "Joint DL / UL TCI” operation, one Joint / DL TCI state can be activated per TCI codepoint. One schematic example of how this may look is illustrated in table 1 . In case the indicated TCI codepoint is "0”, the UE should apply "Joint / DL TCI state 3” as common QCL source for both DL and UL signals / channels. Please note that the word Joint in Joint / DL TCI states means that the TCI states can be used for both DL and UL signals at the same time.

[0069] Table 1 : Example of activated TCI states and their mapping to TCI field codepoints for "Joint DL / UL TCI” operation.

[0070] For "Separate DL / UL TCI” operation up to two TCI states can be activated per TCI codepoint, one for DL sig- nals / channels (Joint / DL TCI state) and one for UL signals / channels (UL TCI state). One schematic example of how this may look is illustrated in table 2. In case the TCI codepoint is "0”, the UE should apply "Joint / DL TCI state 3” as common QCL source for DL signals / channels, and not update the current QCL source for UL signals / channel. In case the TCI codepoint is "7”, the UE should apply "UL TCI state 57” as QCL source for UL signals / channels, and not update the QCL source for DL signals / channel. In case the TCI codepoint is "3”, the UE should apply "Joint / DL TCI state 10” as QCL source for DL signals / channels and apply "UL TCI state 12” as QCL source for UL signals / channels.

[0071] Table 2: Example of activated TCI states and their mapping to TCI field codepoints for "Separate DL / UL TCI” operation.

[0072] For both "Joint DL / UL TCI” and "Separate DL / UL TCI” the large scale QCL properties are inferred from one (QCL- Typel) or two RSs (QCL -Typel and QCL -Type2) analogous to Rel-15 / 16 beam management framework, where the first QCL type can be either QCL Type A, QCL type B or QCL type C, and QCL-Type2 can be QCL type D, as describes above. For "Joint DL / UL TCI”, the UL spatial filter is derived from the RS of DL QCL Type D, analogous to default beam operation for Rel-15 / 16 beam management framework.

[0073] In the DL, the Joint / DL-only TCI state can provide common QCL information for UE-dedicated PDCCH, PDSCH and / or aperiodic CSI-RS. RRC configuration is used to indicate if a non-UE dedicated PDCCH / PDSCH, aperiodic CSI-RS should follow the common beam or not. For DL signal / channels that do not follow the common beam, a Rel-17 TCI state can be indicated as QCL source in a similar way as for Rel-15 / 16 beam management framework. As an example, for a periodic CSI-RS that does not follow the common beam, a Rel-17 TCI state can be configured in the parameter "QCL-Info- PeriodicCSI-RS” in "NZP-CSI-RS-Resource information element” as specified in 3GPP TS 38.331 . Any DL RS that is a valid target DL RS of a Rel-15 / 16 TCI state based on the Rel-15 / 16 beam management framework can be configured as a target DL RS of Rel-17 DL TCI. The possible target and source RS and corresponding QCL properties for Joint / DL TCI states are summarized in

[0074] Table below.

[0075] Table 3: Possible configurations of target and source RS and corresponding QCL properties for Joint / DL TCI states

[0076] In UL, the Joint / DL TCI state (for "Joint DL / UL TCI operation”) or UL TCI state (for "Separate DL / UL TCI” operation) can provide common QCL information for all or a subset of all PUCCH resources, dynamic-grant / configured-grant PUSCH and SRS for all usages (except for usage 'positioning').

[0077] RRC configuration is used to indicate if an SRS or a PUCCH resource should follow the common beam or not. For UL signal / channels that do not follow the common beam, a Rel-17 TCI state can be used to indicate spatial relation instead of a DL / UL-RS which is used to indicate spatial relation for Rel-15 / 16 beam management framework. As an example, for a periodic SRS resource that does not follow the common beam, a new RRC parameter in an SRS resource can be configured with a Rel-17 TCI state, and the UE will use that Rel-17 TCI state to determine the spatial relation for that SRS resource. Any of the following reference signals can be used to indicate spatial relation for a UL signal / channel in Rel-17 TCI state framework: SSB, TRS, CSI-RS for BM, SRS with usage BM.

[0078] Referring to UL Power control, it is noted that, for the unified TCI state framework, a path loss reference signal (PL- RS) is either included in or associated with a TCI state (Joint / DL TCI state or UL TCI state). This means that the PL- RS is automatically updated when the TCI state is updated, which means the MAC-CE update and / or RRC re-config- uration of the PL-RS is not needed when the UE moves around in the cell. Similar to Rel-15 / 16, a PL-RS can be a periodic DL-RS (SSB or periodic CSI-RS).

[0079] For other UL power control parameters except for PL-RS (i.e., PO, alpha, closed loop index), a setting of PO, alpha, closed loop index can be either associated per signal / channel and applied for all TCI states (i.e. for a given UL signal / channel, the same power control parameters are used for all TCI states), or they can be associated per signal / channel per TCI state (i.e. for a given UL signal / channel, different power control parameters can be used for different TCI states). The association between UL power control parameters, UL channels / signals and TCI states is configured via RRC.

[0080] More specifically referring to UL beam management, some UEs could have analog beamformers with poor beam correspondence, which implies that DL / UL reciprocity cannot be used to determine the beams for said beamformers. For such UEs, the UE beam used for UL cannot be derived from beam management procedures based on DL reference signals as described above. To handle such UEs, UL beam management has been included in the NR standard specification since Rel-15. The main difference between DL beam management and UL beam management is that UL beam management utilizes uplink reference UL-RSs instead of DL-RSs. The UL-RS that has been agreed to be used for UL beam management is SRS. Two UL beam management procedures are supported in NR: U2 and U3, which are schematically illustrated in Figure 3. The U2 procedure is performed by transmitting a burst of SRS resources in one UE TX beam and letting the TRP evaluate different TRP RX beams. The U3 procedure lets the UE evaluate a suitable UE TX beam by transmitting different SRS resources in different UE TX beams.

[0081] UL beam management can also be useful even if UEs have beam correspondence. That is, a combined DL beam management procedure and UL beam management procedure requires less overhead and latency compared to only using DL beam management procedures. If the base station has a fully digital receiver it can determine a base station beam based on reciprocity. In this case, the gNB can determine a preferred gNB beam for a certain UE based on a single SRS transmission from that UE (since a digital receiver can evaluate all candidate gNB beams simultaneously). Further than that, "UL only”-node deployments are suitable to improve UL coverage in a cost-efficient way (especially at higher frequencies). An "UL only” network node is equipped with UL capability but with no or limited DL downlink capability. In this case, since the "UL only” node is not capable of transmitting DL reference signals, the beam pair link between a UE and an "UL only” node has to be based on UL beam management procedures.

[0082] In D-MIMO, there will be many different access points (APs) or transmission points (TRPs) in a small area, and where each AP / TRP could be equipped with multiple different beams. In case DL-beam management is used to determine a suitable AP / TRP and corresponding AP / TRP beam to a UE, significant amount of reference -signal overhead is needed, which has been identified as an issue for D-MIMO. To reduce overhead, AP / TRP selection and corresponding beam selection can be based on UL SRS transmission from the UE (which then could be used to determine suitable AP / TRP and corresponding AP / TRP beams for that UE).

[0083] Hence, it is likely that UL beam management will play a more significant role for 5G -Advanced and 6G applications.

[0084] Figure 4 shows a flowchart of a method 100 according to the invention. The method is performed by a user equipment (UE) according to the disclosure in combination with a base station according to the disclosure, wherein the base station is in particular a gNB. The UE is performing a method for the UE according to the dsclosure and the base station is performing a method for a base station according to the disclosure.

[0085] In a first step, the UE is transmitting 101a a support indication to the base station, wherein the support indication is indicating that the UE is capable to determine a beam for receiving the downlink signal and / or the downlink channel based on an uplink reference signal. The base station is receiving 101b the support indication. Optionally, the support indication is indicating a support of DOI based beam indication for the downlink signal and / or the downlink channel based on the uplink reference signal. In this case, the base station is preferably conveying a reference signal indication in one or more fields in a Downlink Control Information (DOI). Optionally, the support indication is indicating a support of MAC-CE based beam indication for the downlink signal and / or the downlink channel based on the uplink reference signal. In this case, the base station is preferably conveying a reference signal indication in one or more fields in a MAC-CE. Optionally, the support indication is indicating a support of RRC based beam indication for the downlink signal and / or the downlink channel based on the uplink reference signal. In this case, the base station is preferably conveying a reference signal indication in one or more fields in a RRC message. Optionally, the support indication is indicating a support of a number of simultaneous beam indications for the downlink signal and / or the downlink channel based on the uplink reference signal.

[0086] In a second step, the base station is transmitting 102a a configuration from the base station, wherein the configuration comprises a definition of uplink reference signal resources (UL-RS resources). The UL-RS resources are resources in time and / or frequency domain of a transmission band and / or a code domain that is used for the communication between the UE and the base station. The code domain preferably defines a type of coding that is applied to the reference signal. The configuration is transmitted if the support indication is indicating that the UE is capable to determine a beam for receiving the downlink signal and / or the downlink channel based on an uplink reference signal. Preferably, if the the support indication is indicating that the UE is not capable to determine a beam for receiving the downlink signal and / or the downlink channel based on an uplink reference signal, the base station is not transmitting the configuration and a different method for determining the beam for receiving the downlink signal and / or the downlink channel is used. The UE receives 102b the configuration from the base station.

[0087] In a third step, the base station is transmitting 103a a trigger to transmit the uplink reference signal to the UE. The trigger is sent after the configuration that comprises the definition of the UL-RS resources has been transmitted. The UE is receiving 103b the trigger.

[0088] In a fourth step, the UE is transmitting 104a an uplink reference signal to the base station on at least one beam using the UL-RS resources that are defined in the received configuration. Preferably, the UE is transmitting the uplink reference signal to the base station on multiple beams, wherein a different UL-RS resource is used on each beam of the UE. Preferably, the uplink reference signal is transmitted to the base station on multiple beams using the UL-RS resources that are defined in the received configuration. Each one of the multiple beams is generated using a different spatial filter so that the beams are transmitted in different spatial directions. The uplink reference signal is transmitted to the base station on the at least one beam in reaction to receiving the trigger. The base station is receiving the uplink reference signal from the UE, using some or all of the uplink reference signal resources that are defined in the received configuration. The base station is receiving the reference signal using multiple beams in parallel and is therefore receiving the uplink reference signal that was transmitted on at least one beam by the UE using some or all of the uplink reference signal resources that are defined in the transmitted configuration. Each UL-RS resource of a received uplink reference signal that is received by the base station and is transmitted by the UE is logically linked to the beam that was used for transmitting the uplink reference signal. The reference signal is received 104b on at least one beam by the base station.

[0089] In a fifth step, the base station determines one or more preferred beams of the at least one beam based on the received uplink reference signal of each beam and transmits 105a a reference signal indication to the UE. The UE receives 105b reference signal indication that was transmitted by the base station.

[0090] In case there is only a single beam received from the UE, the base station determines this beam as the preferred beam. The base station is preferably using the uplink reference signal to determine the preferred beam. For example, a beam of the UE with the highest signal quality of the uplink reference signal is determined to be the preferred beam or a set of beams with the highest signal quality of the uplink reference signal is determined to be the preferred beams. Optionally, the determination of the one or more preferred beams comprises a comparison of a signal quality of the received uplink reference signal that have been transmitted on different beams.

[0091] In the fifth step, the base station further transmits the reference signal indication to the UE, wherein the reference signal indication is indicating at least one UL-RS resource on which the uplink reference signal has been transmitted by the UE to the base station on one of the preferred beams. In case that a single beam has been determined as preferred beam, the reference signal indication is indicating the UL-RS resource that has been used by the UE for transmitting the reference signal on this beam. In case that multiple beams have been determined as preferred beams, the reference signal indication is indicating the UL-RS resources that have been used by the UE for transmitting the reference signal on these beams. The UE is receiving the reference signal indication from the base station. Each UL-RS resource is specific for one beam and the relation between UL-RS resource and the respective beam is known to the UE. Therefore, the base station is indicating preferable beams to the UE with the reference signal indication.

[0092] The reference signal indication is pointing to one or more of the UL-RS resources. For example, the base station is sending a global uplink reference signal resource set ID and a global uplink reference signal resource ID to indicate the UL-RS resources. In another example, the base station is sending a global uplink reference signal resource set ID and a local uplink reference signal resource ID to indicate the UL-RS resources. In another example, the base station is sending a local uplink reference signal resource set ID and a global uplink reference signal resource ID to indicate the UL-RS resources. In another example, the base station is sending a local uplink reference signal resource set ID and a local uplink reference signal resource ID to indicate the UL-RS resources. In another example, the base station is sending only a global uplink reference signal resource ID to indicate the UL-RS resources. In another example, the base station is sending only a semi-Local uplink reference signal resource ID to indicate the UL-RS resources. In another example, the base station is sending only a local uplink reference signal resource ID to indicate the UL-RS resources. The reference signal indication is preferably conveyed in a downlink joint TCI state, also referred to as Joint / DL TCI state, wherein the UL-RS resources are configured as QCL-Type D / spatial relation in the DL / Joint TCI state. In the alternative, the reference signal indication is conveyed in one or more fields in a Downlink Control Information, DCI. In case the reference signal indication is conveyed in one or more fields in a DCI, the one or more fields in DCI for conveying the reference signal indication are preferably included in the DCI based on a Radio Resource Control, RRC, configuration, wherein one, two or more UL-RS resources are indicated in one field in the DCI. A corresponding number of downlink joint TCI states (Joint / DL TCI states) and UL-RS resources are indicated in the one or more fields in the DCI. A QCL Type A, B and / or C is determined for the received downlink signals and / or for the downlink channel from a Joint / DL TCI state, and a spatial filter for the received downlink signal and / or downlink channel is determined based on the indicated UL-RS resource.

[0093] In a sixth step, the base station is transmitting 106a a downlink signal and / or a downlink channel to the UE. For this, the base station is optionally using a beam that has been used by the base station for receiving the uplink reference signal on the UL-RS resource that is indicated in the reference signal indication. Preferably, the base station uses a beam of the base station that is linked to the UL-RS resource that allowed a reception of the uplink reference signal in a highest signal quality, or the base station uses the beams of the base station that are linked to the UL-RS resources that allowed a reception of the uplink reference signal in a highest signal quality. In the alternative, any other technique for determining a beam of the base station for a transmission to the UE can be applied.

[0094] In a seventh step, the UE is receiving 106b the downlink signal and / or the downlink channel using a beam of the UE that is based on the beam that has been used by the UE for transmitting the uplink reference signal on the UL-RS resource that is indicated in the reference signal indication. The UE is referring to the beams that have been used for transmitting the uplink reference signal and identifies one or more beams by the UL-RS resource that has been indicated in the reference signal indication by the base station. The UE configures a transceiver or the UE to receive the downlink signal and / or the downlink channel using the beams that are identified. Optionally, the UE uses only the beam that has been used for transmitting the uplink reference signal on the UL-RS resource that is indicated in the reference signal indication for receiving the downlink signal and / or the downlink channel, or uses only the beams that have been used for transmitting the uplink reference signal on the UL-RS resources that are indicated in the reference signal indication the downlink signal and / or the downlink channel. In the alternative, the beams for receiving the downlink signal and / or the downlink channel are modified by further mechanisms, for example the beams are adapted based on an alignment of the UE.

[0095] Optionally, the UE is configured with intra-band carrier aggregation with multiple serving cells, wherein the UL-RS resources are configured and transmitted in a first serving cell . In this case, the reference signal indication that is pointing at a UL-RS resource is conveyed in the first serving cell . The determined UE beam is then used for more than one serving cell. For this, the UE is configured via RRC with a list of serving cells, wherein the additional serving cells are defined by the list of serving cells. Summarizing the method that has been described in view of Figure 4, the UE signals in the first step, e.g., during UE capability signalling, support for UL-RS based beam indication for DL channels / signal. The UL-RS based beam indication for DL channels / signal can in addition contain one or more of the following information:

[0096] • Support of DCI based beam indication for (at least) DL signals / channels based on UL-RS.

[0097] • Support of MAC-CE based beam indication for (at least) DL signals / channels based on UL-RS.

[0098] • Support of RRC based beam indication for (at least) DL signals / channels based on UL-RS.

[0099] • Support of X number of simultaneous beam indications for (at least) DL signals / channels based on UL-RS.

[0100] In the second step, the base station configures the UE with UL-RS resources, which for example can be an SRS resource set configured with usage ‘beamManagement’ in NR, or some other kind of UL-RS in 6G (and / or configured with some other usage). In the third step, the base station, preferably a gNB, triggers the UE to transmit the UL-RS resources, and in the fourth step, the UE transmits the UL-RS resources in different UE beams. In the fifth step, the base station receives the UL-RS resources, determines a preferred UL-RS resource (e.g., based on highest received RSRP of the RS), and indicates the UL-RS resource to the UE. In the sixth step the base station triggers the UE for DL signals / channel transmission, and the seventh step the UE utilizes a UE beam associated with the indicated UL- RS resource in the previous step.

[0101] For using the method 100 in a NR network, a new rule can be included in the NR specification which allows an UL- RS to be used as QCL Type-D (i.e., spatial QCL, also sometimes referred to as spatial relation) for DL signals / channels, i.e., an UL-RS can be included as spatial QCL in a DL / Joint TCI state. Optionally, a new UE capability signalling is introduced in NR, indicating if a UE is capable of doing this or not. Preferably, as part of this UE capability signaling, the UE might also indicate a new maximum number of supported TCI states where a DL-RS is used to indicate QCL type-A / B / C and an UL-RS is used to indicate QCL Type-D. However, in NR, a DL / Joint TCI state for FR2 needs to consist of two DL-RSs, one used for doppler / delay estimation by the UE (to help the UE receive the DL signals / channels) and another used for spatial relation indication (helping the UE to select a suitable analog beam). Hence, even if an UL-RS in a TCI state is used to indicate the spatial relation, it is still necessary to indicate a DL-RS used for delay / doppler estimation. Since a TRP (transmission point) typically uses around 20 or more SSB beams, and UE might have around 30 to 40 narrow UE beams, the total number of combinations that need to be supported is 20*30 = 600 TCI states, which will require an extensive amount of signalling overhead (RRC and / or MAC / DCI). Hence, further improvement is advantageous.

[0102] Preferable, a UE that is operating in FR2 and is supporting beam indication for DL signals / channels based on UL-RS is configured. The UE can be configured with DL / Joint TCI states that do not include spatial relation (QCL-type D), but only QCL Type A / B / C. In this case, the spatial relation (or spatial QCL / QCL Type-D) will instead be indicated separately to the UE, i.e., the QCL type A / B / C and QCL type D is indicated independently / separately of each other. In the alternative, a DCI can indicate both a TCI state used for Type A / B / C QCL (for example using legacy Transmission configuration indication field in DCI format 1_1 and 1_2) and indicate a spatial QCL by other new field(s) in DCI pointing at an UL-RS resource (e.g., using an SRS resource indicator (SRI) and / or SRS resource set indicator in NR).

[0103] For using the method 100 in a 6G network, separate indications can be used for spatial QCL and other type of QCL (e.g., QCL Type A, B or C in NR), and the two different indications are conveyed using two different types of indicators. Preferably, a first indicator (referred to in this invention disclosure as “DelayDopplerlndicator”) is used to indicate some kind of delay / doppler information (e.g., QCL Type A / B / C) and a second indicator (referred to in this invention disclosure as "SpatialFilterlndicator”) is used to indicate spatial QCL (e.g., QCL Type D). Preferably, each "DelayDopplerlndicator'' can consist of one DL-RS, e.g., an SSB, TRS or similar signals in 6G, which can be used by the UE to determine delay and / or Doppler related information. In one embodiment, the "SpatialFilterlndicator” can be configured with one DL-RS or one UL-RS, and can be used by the UE to determine spatial QCL information.

[0104] For an implementation to NR and 6G networks, it is preferable to use the UL-RS as beam indication for DL sig- nals / channels is supported together with "TRS free operation”. "TRS free operation” will likely be considered as a key component for 6G and entails that the UE can determine QCL type A / B / C from DMRS instead of TRS, which simulations have shown works sufficient well in case the DMRS spans a sufficiently large frequency band. At mmWave frequencies, the frequency band spanned by DMRS is typically rather large, hence this should not be an issue at mmWave frequencies. In this case, a UE that is operating with "TRS free operation”, can be indicated with an UL-RS for spatial QCL and then use DMRS to determine delay and doppler related information, e.g., QCL Type A / B / C. Preferably, the spatial QCL is indicated in a field in DCI. The field in DCI can for example be a new field used only for the purpose of indicating spatial QCL to a UE or be an old field that is re-purposed (for example the legacy NR Transmission configuration indication field in DCI format 1_1 and 1_2 can be re-used for this purpose).

[0105] How the UL-RS is indicated to the UE in DCI / MAC-CE can be done in multiple different ways. Some of these ways are indicating:

[0106] • Global UL-RS resource set ID (or UE panel index) and Global UL-RS resource ID (note that Global ID here for example can refer to an ID that is unique per serving cell, per serving cell group, per band width part (BWP) etc.).

[0107] • Global UL-RS resource set ID (or UE panel index) and Local UL-RS resource ID (i.e., the index is based on the position of the UL-RS resource in the indicated UL-RS resource set or indicate UE panel index).

[0108] • Local UL-RS resource set ID (i.e., the index is pointing at one out of the UL-RS resource sets configured with usage beam management) and Global UL-RS resource ID.

[0109] • Local UL-RS resource set ID (i.e., the index is pointing at one out of the UL-RS resource sets configured with usage beam management) and Local UL-RS resource ID (i.e., the index is based on the position of the UL-RS resource in the indicated UL-RS resource set).

[0110] • Only Global UL-RS resource ID (could for example be used in case different UL-RS resources are configured in different UL-RS resource sets). • Only Semi-Local UL-RS resource ID (i.e. , the index is based on the position of the UL-RS resource in one or more UL-RS resource sets configured with usage beam management).

[0111] • Only Local UL-RS resource ID (i.e., the index is based on the position of the UL-RS resource in the last transmitted UL-RS resource set configured with usage beam management).

[0112] Preferably, for a UE configured with intra-band carrier aggregation with multiple serving cells, and where a set of UL- RSs used for beam management are configured and transmitted in a first serving cell, and where the associated beam indication pointing to one of the transmitted UL-RSs is conveyed to the UE in a DCI / MAC-CE in the first serving cell, the UE determines spatial QCL based on the indicated UL-RS for DL signals / channels belonging to the first serving cell and for DL signals / channels belonging to one or more of the remaining serving cells (for the intra-band carrier aggregation). This could be used to save beam management overhead signaling, since the UE can determine spatial QCL for multiple serving cells based on beam management procedures and beam indication in only one serving cell. Preferably, the UE is RRC configured with a list of serving cells that the UE should determine the UE beam for based on the indicated beam (UL-RS resource) from one of the serving cells (for example the UE could be configured with a list of serving cells that should follow the indicated UL-RS resource in the first serving cell).

[0113] Figure 5 is illustrating an exemplary structure of a UE 10 according to the invention. The UE comprises a processing circuitry 11, a memory 12 and a transceiver 13. The memory 12 contains instructions, which when executed by said processing circuitry 11, causes the UE 10 to receive a configuration from a base station, the configuration comprising a definition of uplink reference signal resources, also referred to as UL-RS resources, transmit an uplink reference signal to the base station on at least one beam using the UL-RS resources that are defined in the received configuration, receive a reference signal indication from the base station, wherein the reference signal indication is indicating at least one UL-RS resource that has been used for transmitting the uplink reference signal; and receive a downlink signal and / or a downlink channel using a beam that is based on the beam that has been used for transmitting the uplink reference signal on the UL-RS resource that is indicated in the reference signal indication. More specifically, the memory 12 contains instructions, which when executed by said processing circuitry 11 , causes the UE 10 to act as the UE that is involved with performing the method of Figure 4.

[0114] Figure 6 is illustrating an exemplary structure of base station 20 according to the invention. The base station 20 comprises a processing circuitry 21, a memory 22 and a transceiver 23. The memory 22 contains instructions, which when executed by said processing circuitry 21 causes the base station 20 to transmit a configuration to a user equipment, UE, the configuration comprising a definition of uplink reference signal resources, receive an uplink reference signal from the UE on at least one beam, using some or all of the uplink reference signal resources that are defined in the received configuration, determine one or more preferred beams of the at least one beam based on the received uplink reference signal of each beam; and transmit a reference signal indication to the UE, wherein the reference signal indication is indicating at least one UL-RS resource that has been used for receiving the uplink refer- ence signal on one of the preferred beams. More specifically, the memory 22 contains instructions, which when executed by said processing circuitry 21, causes the base station 10 to act as the base station that is involved with performing the method of Figure 4.

[0115] Figure 7 is illustrating an exemplary system 40 according to the invention. The system comprises a UE 10 and a base station 20 according to the invention.

[0116] Figure 8 is illustrating a communication system 41 according to the invention. The communication system includes a host computer 42 comprising processing circuitry 43 configured to provide user data and a communication interface 44 configured to forward the user data to a cellular network for transmission to the user equipment UE 10, wherein the cellular network comprises the base station 20 having a radio interface, in particular the transceiver 23, and the processing circuitry 21. The base station's 20 processing circuitry 21 is configured to perform the method 100 for the base station 20. The UE 10 comprises a radio interface, in particular the transceiver 13, and the processing circuitry 11.

[0117] The processing circuitry 43 of the host computer 42 is configured to execute a host application, thereby providing the user data; and the UE 10 comprises processing circuitry 11 configured to execute a client application associated with the host application. Such a communication system is efficiently using availably radio resources, allowing that any data that is to be communicated from the host computer to the UE is reliably communicated, even if the UE is in an environment with limited availability of radio resources.

Claims

Claims1. A method (100) for a User Equipment, UE (10), the method comprising: receiving (102b) a configuration transmitted by a base station (20), the configuration comprising a definition of uplink reference signal resources, also referred to as UL-RS resources; transmitting (104a) an uplink reference signal to the base station on at least one beam using the UL-RS resources that are defined in the received configuration; receiving (105b) a reference signal indication transmitted by the base station, wherein the reference signal indication is indicating at least one UL-RS resource that has been used for transmitting the uplink reference signal; and receiving (106b) a downlink signal and / or a downlink channel using a beam that is based on the beam that has been used for transmitting the uplink reference signal on the UL-RS resource that is indicated in the reference signal indication.

2. The method (100) according to claim 1, wherein the uplink reference signal is transmitted to the base station on multiple beams using the UL-RS resources that are defined in the received configuration.

3. The method (100) according to any one of the previous claims, further comprising: receiving (103b) a trigger from the base station to transmit the uplink reference signal; wherein the uplink reference signal is transmitted to the base station on the at least one beam in reaction to receiving the trigger.

4. The method (100) according to any one of the previous claims, further comprising: transmitting (101a) a support indication to the base station, wherein the support indication is indicating that the UE (10) is capable to determine a beam for receiving the downlink signal and / or the downlink channel based on the uplink reference signal.

5. The method (100) according to claim 4, wherein the support indication is indicating a support of the UE (10) of one or more of the following:- Support of DCI based beam indication for the downlink signal and / or the downlink channel based on the uplink reference signal;- Support of MAC-CE based beam indication for the downlink signal and / or the downlink channel based on the uplink reference signal;- Support of RRC based beam indication for the downlink signal and / or the downlink channel based on the uplink reference signal;- Support of a number of simultaneous beam indications for the downlink signal and / or the downlink channel based on the uplink reference signal.

6. The method (100) according to any one of the previous claims, wherein the reference signal indication is pointing to one or more of the UL-RS resources, preferably by using:- a global uplink reference signal resource set ID and a global uplink reference signal resource ID,- a global uplink reference signal resource set ID and a local uplink reference signal resource ID,- a local uplink reference signal resource set ID and a global uplink reference signal resource ID,- a local uplink reference signal resource set ID and a local uplink reference signal resource ID,- only a global uplink reference signal resource ID,- only a semi-Local uplink reference signal resource ID, or- only a local uplink reference signal resource ID.

7. The method (100) according to any one of the previous claims, wherein the reference signal indication is conveyed in a downlink joint TCI state, also referred to as Joint / DL TCI state, and wherein the UL-RS resources are configured as QCL-Type D / spatial relation in the DL / Joint TCI state.

8. The method (100) according to any one of claims 1 to 6, wherein the reference signal indication is conveyed in one or more fields in a Downlink Control Information, DCI.

9. The method (100) according to claim 8, wherein the one or more fields in DCI for conveying the reference signal indication are included in the DCI based on a Radio Resource Control, RRC, configuration.

10. The method (100) according to claim 9, wherein two or more UL-RS resources are indicated in one field in the DCI.

11. The method (100) according to claim 10, wherein a corresponding number of downlink joint TCI states, also referred to as Joint / DL TCI states, and UL-RS resources are indicated in the one or more fields in the DCI.

12. The method (100) according to any one of the previous claims 9 to 11, wherein a QCL Type A, B and / or C is determined for the received downlink signals and / or for the downlink channel from a Joint / DL TCI state, and a spatial filter for the received downlink signal and / or downlink channel is determined based on the indicated UL-RS resource.

13. The method (100) according to any one of the previous claims, wherein the UE (10) is configured with intra-band carrier aggregation with multiple serving cells, wherein the UL-RS resources are configured and transmitted in a first serving cell, wherein the reference signal indication that is pointing at the at least one UL-RS resource is conveyed in the first serving cell, and wherein the determined UE beam is used for more than one serving cell .

14. The method (100) according to claim 13, wherein the UE (10) is configured via RRC with a list of serving cells, wherein the additional serving cells are defined by the list of serving cells.

15. A user equipment, UE (10), comprising a processing circuitry (11), a memory (12) and a transceiver (13), wherein said memory (12) contains instructions, which when executed by said processing circuitry (11) causes the UE (10) to: receive (102b) a configuration from a base station (20), the configuration comprising a definition of uplink reference signal resources, also referred to as UL-RS resources; transmit (104a) an uplink reference signal to the base station on at least one beam using the UL-RS resources that are defined in the received configuration; receive (105b) a reference signal indication from the base station, wherein the reference signal indication is indicating at least one UL-RS resource that has been used for transmitting the uplink reference signal; and receive (106b) a downlink signal and / or a downlink channel using a beam that is based on the beam that has been used for transmitting the uplink reference signal on the UL-RS resource that is indicated in the reference signal indication.

16. The UE (10) according to claim 15, wherein the UE (10) is further is configured to perform the method of any of claims 2 to 14.

17. A method (100) for a base station (20), the method comprising: transmitting (102a) a configuration to a user equipment, UE (10), the configuration comprising a definition of uplink reference signal resources; receiving (104b) an uplink reference signal from the UE (10) that was transmitted on at least one beam by the UE, using some or all of the uplink reference signal resources that are defined in the transmitted configuration; and determining (105a) one or more preferred beams of the at least one beam based on the received uplink reference signal of each received beam, and transmitting a reference signal indication to the UE, wherein the reference signal indication is indicating at least one UL-RS resource on which the uplink reference signal has been transmitted by the UE on one of the preferred one or more beams.

18. The method (100) according to claim 17, further comprising: transmitting (103a) a trigger to the UE (10), wherein the trigger is for triggering a transmission of the uplink reference signal on at least one beam by the UE (10).

19. The method (100) according to any one of the previous claims 17 or 18, further comprising: receiving (101b) a support indication that was transmitted by the UE (10), wherein the support indication is indicating that the UE (10) is capable to determine a beam for receiving the downlink signal and / or the downlink channel based on the uplink reference signal, and performing the determining (105a) of one or more preferred beams of the at least one beam and transmitting the reference signal indication to the UE if the support indication was received.

20. A base station (20) comprising a processing circuitry (21), a memory (22) and a transceiver (23), wherein said memory (22) contains instructions, which when executed by said processing circuitry (21) causes the base station (20) to: transmit (102a) a configuration to a user equipment, UE, the configuration comprising a definition of uplink reference signal resources; receive (104b) an uplink reference signal from the UE that was transmitted on at least one beam by the UE using some or all of the uplink reference signal resources that are defined in the transmitted configuration; and determine (105a) one or more preferred beams of the at least one beam based on the received uplink reference signal of each received beam and transmit a reference signal indication to the UE, wherein the reference signal indication is indicating at least one UL-RS resource on which the uplink reference signal has been transmitted by the UE on one of the one or more preferred beams.21 . The base station (20) according to claim 20, wherein the base station (20) is further is configured to perform the method of any of claims 18 or 19.

22. A system comprising a base station according to claim 20 and a UE according to claim 15.

23. A method (100) for a system (40) that comprises a User Equipment, UE (10), and a base station (20), the method comprising: transmitting (102a), by the base station (20), a configuration to the UE (10), the configuration comprising a definition of uplink reference signal resources, also referred to as UL-RS resources; transmitting (104a), by the UE (10) an uplink reference signal to the base station (20) on at least one beam using the UL-RS resources that are defined in the received configuration, wherein the uplink reference signal is received by the base station (20) from the UE (10) by using some or all of the uplink reference signal resources that are defined in the transmitted configuration; determining (105a), by the base station (20), one or more preferred beams of the at least one beam based on the received uplink reference signal of each received beam and transmitting a reference signal indication to the UE(10), wherein the reference signal indication is indicating at least one UL-RS resource on which the uplink reference signal has been transmitted by the UE (10) on one of the preferred one or more beams; transmitting (106a), by the base station (20), a downlink signal and / or a downlink channel to the UE (10); and receiving (106b), by the UE (10), the downlink signal and / or the downlink channel using a beam that is based on the beam that has been used for transmitting the uplink reference signal on the UL-RS resource that is indicated in the reference signal indication.

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