EP4690499A1

EP4690499A1 - Technique enabling initial transmission beam selection for a sidelink connection

Info

Publication number: EP4690499A1
Application number: EP24714937.0A
Authority: EP
Inventors: Jan Christoffersson; Min Wang; Zhang Zhang
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2023-04-06
Filing date: 2024-03-26
Publication date: 2026-02-11
Also published as: WO2024208652A1

Abstract

The present disclosure provides for a method performed by a first wireless device configured to communicate with a second wireless device over a sidelink connection, the method comprising: transmitting first information over a plurality of transmission, Tx, beams; receiving, from the second wireless device, second information indicative of at least one beam measurement result for at least one of the Tx beams; and selecting, based on the second information, one of the plurality of Tx beams as an initial Tx beam to be used by the first wireless device for the sidelink connection. The present disclosure also provides for a corresponding method performed by the second wireless device. The present disclosure also provides for a first and a second wireless device, a communication system and storage media.

Description

Technique enabling initial transmission beam selection for a sidelink connection

TECHNICAL FIELD

The present disclosure generally relates to a method performed by a first wireless device configured to communicate with a second wireless device over a sidelink connection. The present disclosure also relates to a method performed by a second wireless device configured to communicate with a first wireless device over a sidelink connection. A first wireless device and a second wireless device, a communication system and storage media are also disclosed.

BACKGROUND

In a communication system, a wireless device such as a mobile user equipment (UE) may communicate with a base station. Modern base stations can transmit information over a plurality of transmission, Tx, beams toward one or more wireless devices. Previous works focused on selecting suitable Tx beams for transmitting downlink (DL) data from a base station to a wireless device. Wireless devices may also support beam-based transmission of uplink (UL) data to base stations.

In recent years, connectivity of wireless devices has become of increasing importance. Wireless devices may communicate with one another over so-called Device-to-Device (D2D) or sidelink (SL) connections.

SUMMARY

A Tx beam may be used by a wireless device for directly transmitting data over a SL connection to another wireless device. There is a need for a technique enabling selection of a Tx beam for a SL connection.

According to a first aspect, a method performed by a first wireless device configured to communicate with a second wireless device over a sidelink connection is provided. The method comprises transmitting first information over a plurality of transmission, Tx, beams. The method comprises receiving, from the second wireless device, second information indicative of at least one beam measurement result for at least one of the Tx beams. The method further comprises selecting, based on the second information, one of the plurality of Tx beams as an initial Tx beam to be used by the first wireless device for the sidelink connection.

The method may further comprise, after having selected the initial Tx beam, at least one of the following steps: establishing the sidelink connection between the first wireless device and the second wireless device; transmitting data via the initial Tx beam to the second wireless device. The step of transmitting the first information may be triggered when at least one of the following conditions is met: the first wireless device receives data to be transmitted towards the second wireless device; the first wireless device determines that the second wireless device is configured to receive and/or transmit information over a sidelink connection; a sidelink connection needs to be established between the first wireless device and the second wireless device; the first wireless device receives a request from the second wireless device to select an initial Tx beam and/or establish a sidelink connection between the first wireless device and the second wireless device; a link establishment procedure for establishing a sidelink connection between the first wireless device and the second wireless device is started; the first wireless device receives a link establishment acknowledgement from the second wireless device. The first wireless device may determine that the second wireless device is configured to receive and/or transmit information over a sidelink connection based on at least one of the following: requirement information indicating that a sidelink transmission and/or reception needs to be performed using a sidelink carrier requiring beamforming; capability information obtained from the second wireless device. The requirement information may be preconfigured at the first wireless device or configured by a base station. The method may further comprise receiving the requirement information from the base station. The capability information may indicate that the second wireless device supports beamforming based sidelink transmission and/or reception.

The first information may be beam-specific. The first information transmitted over the plurality of Tx beams may differ between at least two of the Tx beams. The first information may be indicative of the respective Tx beam and/or indicative of an index or identifier of the respective Tx beam. The first information may be indicative of an identity, ID, of the first wireless device. The ID of the first wireless device may be included in the first information or derivable from the first information. The ID of the first wireless device may be a layer two, L2, ID of the first wireless device or a local ID associated with a layer two, L2, ID of the first wireless device. The ID of the first wireless device may be derivable from the first information using a mapping between the ID of the first wireless device and at least a portion of the first information. The ID of the first wireless device may be a local ID associated by a mapping to a layer two, L2, ID of the first wireless device. The mapping may be a mapping is between a layer two, L2, ID of the first wireless device and a Sidelink Synchronization Signal Identity, SLSS ID. The SLSS ID may be assigned or selected during an initial L2 link establishment. The mapping may be preconfigured. The method may further comprise transmitting the mapping or information indicative of the mapping to the second wireless device. The mapping or the information indicative of the mapping may be transmitted in a discovery message or in a link establishment request message. The ID of the first wireless device may be part of a Master Information Block, MIB.

At least one of the first information and the second information may be carried by one or more of the following resources or signals: Medium Access Control, MAC, Control Element, MAC CE; Sidelink Control Information, SCI; Sidelink Synchronization Signal Block, SL-SSB; Physical Broadcast Channel, PBCH; a Sidelink Reference Signal, SL RS, such as a Sidelink Channel State Information-Reference Signal, SL CSI-RS; one or more sidelink resources carrying a Physical Sidelink Shared Channel, PSSCH, transmission; one or more sidelink resources carrying a Physical Sidelink Control Channel, PSCCH, transmission.

One or more resources for transmitting the first information may be selected from a set of configured resources. The one or more resources may be selected based on an identity, ID, of the first wireless device and/or an identity, ID, of the second wireless device. Each of the configured resources may have an associated resource index, and the one or more resources may be selected based on the associated resource index or indices. The associated index or indices may be determined as result(s) of a formula using the identity, ID, of the first wireless device and/or the identity of the second wireless device as input parameter(s). The one or more resources may be randomly selected from the set of configured resources. The one or more resources may be selected by the first wireless device.

The one or more resources may be selected by a base station. The method may further comprise receiving, from the base station, an indication of the selected one or more resources. The method may further comprise transmitting, to the base station, a request for a selection of one or more configured resources. The set of configured resources may be configured by a base station. The method may further comprise receiving, from the base station, an indication of the set of configured resources. The set of configured resources may be indicated by at least one of the following: system information; master information; Radio Resource Control, RRC, signaling; MAC CE; layer one, LI, signaling. The method may further comprise transmitting, to the base station, a request for configuring the set of configured resources.

The plurality of Tx beams may be determined based on a location of the second wireless device. The plurality of Tx beams may be determined by the first wireless device. The initial Tx beam may be selected based on a location of the second wireless device. The location of the second wireless device may be obtained based on at least one of the following: a Tx beam previously used by the first wireless device in a transmission to the second wireless device; a reception, Rx, beam previously used by the first wireless device in a reception from the second wireless device; location information. The location information may be indicative of at least one of the following: a previous location of the second wireless device; a current or previous movement velocity of the second wireless device; a current or previous movement path of the second wireless device; information indicative of a regular behavior of the second wireless device.

The location information may be indicative of or based on a prediction of the location of the second wireless device. The prediction of the location of the second wireless device may be based on at least one of the following: a previous location of the second wireless device; a current or previous movement velocity of the second wireless device; a current or previous movement path of the second wireless device; information indicative of a regular behavior of the second wireless device. The prediction may be determined by an artificial intelligence module and/or a trained machine learning model.

The location information may be obtained by the first wireless device from at least one of the following entities: the second wireless device; a third wireless device; a base station. The location information may comprise at least one of the following: a position of the second wireless device determined using a global navigation satellite system, GNSS; an identity, ID, of a cell serving the second wireless device; an identity, ID, of a base station serving the second wireless device; one or more position measurement results. The one or more position measurement results may comprise at least one of the following: a Time Difference of Arrical, TDOA; a Round Trip Time, RTT; a Multi-Round Trip Time, Multi-RTT; an Angle of departure, AoD; an Angle of Arrival, AoA.

The second information may be received on one or more resources associated with one of the plurality of Tx beams, and the one of the plurality of Tx beams may be selected as the initial Tx beam. The plurality of Tx beams may consist of multiple subsets of Tx beams and the first wireless device may transmit the first information over one subset of Tx beams at a time. The first wireless device may transmit the first information over different Tx beams of the plurality of Tx beams at different time instants. The first wireless device may transmit the first information over the plurality of Tx beams by transmitting the first information over one Tx beam at a time. The first wireless device may perform beam sweeping to transmit the first information over the plurality of Tx beams.

Each of two or more of the plurality of Tx beams may extend into a beam-specific spatial direction. Each of the plurality of Tx beams may extend into a beam-specific spatial direction. The first information may be transmitted such that the first information is provided to different spatial positions. The first information may be transmitted such that the first information is provided to the different spatial positions at different times. Each of the different spatial positions may be associated with at least one of the plurality of Tx beams. At least two of the different spatial positions may be associated with a same one of the plurality of Tx beams. The first information may be transmitted to the at least two of the different spatial positions using different frequency resources. At least two of the different spatial positions may be associated with different ones of the plurality of Tx beams. An association between the plurality Tx beams and the spatial positions may be preconfigured. An association between the plurality of Tx beams and the spatial positions may be determined and/or dynamically adapted by the first wireless device. The first information may be transmitted for one or more of the spatial positions over a plurality of slots or Orthogonal Frequency-Division Multiplexing, OFDM, symbols.

The first information may be transmitted within a time window. The method may further comprise: indicating, to the second wireless device, at least one temporal location associated with the time window. The at least one temporal location may comprise one or more of: a start time of the time window; a halftime of the time window; an end time of the time window. The first wireless device may indicate the at least one temporal location associated with the time window by transmitting, to the second wireless device, a first SL-SSB or CSI-RS in a SL-SSB or CSI-RS resource associated with the at least one temporal location. The first wireless device may indicate the at least one temporal location associated with the time window by transmitting, to the second wireless device, a first SL-SSB or CSI-RS using a SL-SSB or CSI-RS sequence associated with the at least one temporal location. The first wireless device may indicate the at least one temporal location associated with the time window by transmitting a message to the second wireless device, the message including a bit or flag indicative of the at least one temporal location. The message may comprise one or more of: Sidelink Control Information, SCI; Medium Access Control, MAC, Control Element, MAC CE; Medium Access Control Protocol Data Unit, MAC PDU, header. A length of the time window and/or a number of emissions in the time window may be preconfigured. The time window, including the emission of the first information, may be repeated at least twice. The time window, including the emission of the first information, may be repeated periodically.

Resources used for transmitting the first information and/or the second information may differ from other resources that fulfil at least one of the following criteria: the other resources are used in a sidelink connection of the first wireless device; the other resources are used in a sidelink connection of the second wireless device; the other resources are used in a selection of a non-initial beam. The resources used for transmitting the first information and/or the second information may differ from the other resources in at least one of a time domain and a spatial domain. Transmission time points used for transmitting the first information and/or the second information may differ, by a time offset, from transmission time points used for transmitting and/or receiving information via the sidelink connection. The method may further comprise: indicating, to the second wireless device, a mapping between the time offset and an identity, ID, of the first wireless device. The mapping may be included in at least one of: a discovery message transmitted to the second wireless device from the first wireless device; a sidelink establishment request message transmitted to the second wireless device from the first wireless device. Resources used for transmitting the first information and/or the second information may be specific for the pair of the first wireless device and the second wireless device.

The first information may be transmitted using the same resources as used for receiving the second information. The same resources may exclusively used by the first wireless device during a first time period and exclusively used by the second wireless device during a second time period differing from the first time period. The first time period and the second time period may timely disjunct or separated. The method may further comprise: indicating at least one of the first time period and the second time period to the second wireless device. The at least one of the first time period and the second time period may indicated in one or more of the following: a Sidelink Master Information Block, SL-MIB; a discovery request; a link establishment request; an acknowledgement message. The second time period may start upon or after at least one of the following conditions being fulfilled: the first wireless device has received the second information; the first wireless device has received, from the second wireless device, a Channel State Information, CSI, report; the first wireless device has selected the initial Tx beam. The method may further comprise: transmitting an indication to the second wireless device that an initial Tx beam is to be selected by the first wireless device and/or that measurements of the Tx beams are to be performed by the second wireless device. Transmitting the indication may comprise transmitting, to the second wireless device, at least one of the following: a Medium Access Control, MAC, Control Element, MAC CE; a MAC CE without any accompanying data; a link establishment request; a direct communication request; a PC5 signaling; a PC5-Radio Resource Control, -RRC, signaling; a layer one, LI, signaling. The LI signaling may carried on a physical channel other than Physical Sidelink Shared Channel, PSSCH, Physical Sidelink Control Channel, PSCCH, and Physical Sidelink Feedback Channel, PSFCH. Receiving the second information may trigger selecting the initial Tx beam.

According to a second aspect, a first wireless device is provided. The first wireless device is configured to communicate with a second wireless device over a sidelink connection. The first wireless device is configured to: transmit first information over a plurality of transmission, Tx, beams; receive, from the second wireless device, second information indicative of at least one beam measurement result for at least one of the Tx beams; and select, based on the second information, one of the plurality of Tx beams as an initial Tx beam to be used by the first wireless device for the sidelink connection. The first wireless device may be configured to perform the method according to the first aspect. The first wireless device may comprise at least one processor and at least one memory, the at least one memory storing instructions which, when executed by the at least one processor, cause the at least one processor to perform the method according to the first aspect.

According to a third aspect, a method performed by a second wireless device configured to communicate with a first wireless device over a sidelink connection is provided. The method comprises performing measurements of at least one of a plurality of transmission, Tx, beams of the first wireless device, the plurality of Tx beams transmitting first information. The method further comprises transmitting, to the first wireless device, second information indicative of at least one beam measurement result obtained by performing the measurements of the at least one of the plurality of Tx beams.

The second information may enable the first wireless device to select, based on the second information, one of the plurality of Tx beams as an initial Tx beam to be used by the first wireless device for the sidelink connection. Transmitting the second information may trigger selection of the initial Tx beam by the first wireless device. The second wireless device, after having transmitted the second information, may perform at least one of the following steps: establishing the sidelink connection between the first wireless device and the second wireless device; receiving data via the initial Tx beam from the first wireless device. The second wireless device, before performing the measurements, may perform at least one of the following steps: indicating, to the first wireless device, that the second wireless device is configured to receive and/or transmit information over a sidelink connection; transmitting a request to the first wireless device to select an initial Tx beam and/or establish a sidelink connection between the first wireless device and the second wireless device; transmitting a link establishment acknowledgement to the first wireless device. Indicating, to the first wireless device, that the second wireless device is configured to receive and/or transmit information over a sidelink connection may comprise: transmitting, to the first wireless device, capability information. The capability information may indicate that the second wireless device supports beamforming based sidelink transmission and/or reception. Performing the at least one step may trigger the first wireless device to transmit the first information over the plurality of Tx beams.

The second wireless device may receive the first information over one or more of the plurality of Tx beams. The first information may be beam-specific. The first information received over Tx beams that are measured by the second wireless device may differ between at least two of the measured Tx beams. The first information may be indicative of the respective Tx beam and/or indicative of an index or identifier of the respective Tx beam. The first information may be indicative of an identity, ID, of the first wireless device. The ID of the first wireless device may be included in the first information or derivable from the first information. The ID of the first wireless device may be a layer two, L2, ID of the first wireless device or a local ID associated with a layer two, L2, ID of the first wireless device. The ID of the first wireless device may be derived by the second wireless device from the first information using a mapping between the ID of the first wireless device and at least a portion of the first information. The ID of the first wireless device may be a local ID associated by a mapping to a layer two, L2, ID of the first wireless device. The mapping may be a mapping is between a layer two, L2, ID of the first wireless device and a Sidelink Synchronization Signal Identity, SLSS ID. The SLSS ID may be assigned or selected during an initial L2 link establishment. The mapping may be preconfigured. The method may further comprise: receiving the mapping or information indicative of the mapping from the first wireless device. The mapping or the information indicative of the mapping may be received in a discovery message or in a link establishment request message. The ID of the first wireless device may be part of a Master Information Block, MIB.

One or more resources for transmitting the second information may be selected from a set of configured resources. Each configured resource may span one or more first elements in a frequency domain and one or more second elements in a time domain. The one or more first elements may comprise at least one of: Physical Resource Blocks, PRBs; sub carriers; sub channels, he one or more second elements may comprise at least one of: Orthogonal Frequency Division Multiplexing, OFDM, symbols; slots. The configured resources may be consecutively or non-consecutively distributed in at least one of frequency and time. The configured resources may be configured for the second wireless device and at least one third wireless device. The configured resources may be configured for all wireless devices within a predefined spatial area. The set or a subset of the configured resources may be associated with at least one identity, ID, of a wireless device. The set or a subset of the configured resources may be associated with one or more layer two, L2, destination IDs. The one or more resources may be selected based on one or more of: an identity, ID, of the first wireless device; an identity, ID, of the second wireless device; an index of one or more of the Tx beams of the first wireless device; an indication of the one or more resources, the indication being received by the second wireless device. The one or more of the Tx beams may include a strongest Tx beam measured by the second wireless device. The one or more of the Tx beams may correspond to all Tx beams measured by the second wireless device and having a measured signal strength above a predefined strength threshold. The method may further comprise: receiving the indication of the one or more resources from the first wireless device. The selected one or more resources may be associated with the measured Tx beams having a measured signal strength above a predefined strength threshold. Each of the configured resources may have an associated resource index, and the one or more resources may be selected based on the associated resource index or indices. The associated index or indices may be determined as result(s) of a formula using, as input parameter(s), at least one of the following: an identity, ID, of the first wireless device; an identity, ID, of the second wireless device; an index of one or more of the Tx beams of the second wireless device. The one or more of the Tx beams may include a strongest Tx beam measured by the second wireless device. The one or more of the Tx beams may correspond to all measured Tx beams having a measured signal strength above a predefined strength threshold. The associated index of the one or more configured resources, CRI, to be selected may be determined as a result of the following formula:

CRI = F (UE1_ID, UE2_ID, BI) mod (N), wherein F denotes a mathematical function, UE1_ID denotes the ID of the first wireless device, UE2_ID denotes the ID of the second wireless device and BI denotes the index of the at least one Tx beam measured by the second wireless device, and N denotes a total number of the set of configured resources.

The one or more selected resources may be associated with and/or indicated by a strongest Tx beam measured by the second wireless device. The one or more selected resources may be associated with and/or indicated by all measured Tx beams having a measured signal strength above a predefined strength threshold. Different ones or subsets of the configured resources may be unique for different ones of the Tx beams.

The one or more resources may be randomly selected from the set of configured resources.

The one or more resources may be selected by the second wireless device. The set of configured resources may be configured by a base station. The method may further comprise: receiving, from the base station, an indication of the set of configured resources. The set of configured resources may be indicated by at least one of the following: system information; master information; Radio Resource Control, RRC, signaling; MAC CE; layer one, LI, signaling.

The method may further comprise: selecting, by the second wireless device, one or more Tx beams of the second wireless device; and transmitting the second information over the selected one or more Tx beams of the second wireless device. The one or more Tx beams of the second wireless device may be selected based on a measurement report of the first wireless device indicative of measurement results of measurements of the Tx beams of the second wireless device. The second wireless device may perform beam sweeping to select the one or more of the Tx beams of the second wireless device. The second wireless device may select the one or more Tx beams based on corresponding reception, Rx, beams of the second wireless device used to receive the first information from the first wireless device. The second wireless device may be configured to select the one or more Tx beams based on beam correspondence.

The measurements may be performed in a first time slot and the second information may be transmitted in a second time slot different from the first time slot. The first time slot and the second time slot may fulfil at least one of the following criteria: they are timely disjunct; they are separated in time; they are non-overlapping. The second information may be transmitted when the transmission of the first information over the plurality of Tx beams of the first wireless device is finished. The second information may be transmitted after each time the transmission of the first information over the plurality of Tx beams of the first wireless device is finished. The second information may be transmitted when a beam sweep by the first wireless device using the plurality of Tx beams of the first wireless device is finished. The second information may be transmitted after each time a beam sweep by the first wireless device using the plurality of Tx beams of the first wireless device is finished. The second information may be transmitted after each measurement of a beam strength of the Tx beams of the first wireless device that is performed by the second wireless device. The second information may be transmitted when a beam strength of a Tx beam of the first wireless device that is measured by the second wireless device is above a predefined strength threshold.

The method may further comprise transmitting location information to at least one of: the first wireless device; a third wireless device; a base station. The location information may be indicative of at least one of the following: a previous location of the second wireless device; a current or previous movement velocity of the second wireless device; a current or previous movement path of the second wireless device; information indicative of a regular behavior of the second wireless device.

The location information may comprise at least one of the following: a position of the second wireless device determined using a global navigation satellite system, GNSS; an identity, ID, of a cell serving the second wireless device; an identity, ID, of a base station serving the second wireless device; one or more position measurement results. The one or more position measurement results may comprise at least one of the following: a Time Difference of Arrical, TDOA; a Round Trip Time, RTT; a MultiRound Trip Time, Multi-RTT; an Angle of departure, AoD; an Angle of Arrival, AoA.

The plurality of Tx beams may consist of multiple subsets of Tx beams and the second wireless device may receive the first information over one subset of Tx beams at a time. The second wireless device may receive the first information over different Tx beams of the plurality of Tx beams at different time instants. The second wireless device may receive the first information over the plurality of Tx beams by receiving the first information over one Tx beam at a time.

The first information may be received within a time window. The method may further comprise: receiving, from the first wireless device, an indication of at least one temporal location associated with the time window. The at least one temporal location may comprise one or more of: a start time of the time window; a halftime of the time window; an end time of the time window. Receiving the indication of the at least one temporal location associated with the time window may comprise receiving, from the first wireless device, a first SL-SSB or CSI-RS in a SL-SSB or CSI-RS resource associated with the at least one temporal location. Receiving the indication of the at least one temporal location associated with the time window may comprise receiving, from the first wireless device, a first SL-SSB or CSI-RS using a SL-SSB or CSI-RS sequence associated with the at least one temporal location. Receiving the indication of the at least one temporal location associated with the time window may comprise receiving, from the first wireless device, a message including a bit or flag indicative of the at least one temporal location. The message may comprise one or more of: Sidelink Control Information, SCI; Medium Access Control, MAC, Control Element, MAC CE; Medium Access Control Protocol Data Unit, MAC PDU, header.

A length of the time window and/or a number of emissions in the time window may be preconfigured. The time window, including the reception of the first information, may be repeated at least twice. The time window, including the reception of the first information, may be repeated periodically. Resources used for transmitting the first information and/or the second information may differ from other resources that fulfil at least one of the following criteria: the other resources are used in a sidelink connection of the first wireless device; the other resources are used in a sidelink connection of the second wireless device; the other resources are used in a selection of a non-initial beam. The resources used for transmitting the first information and/or the second information may differ from the other resources in at least one of a time domain and a spatial domain. Transmission time points used for transmitting the first information and/or the second information may differ, by a time offset, from transmission time points used for transmitting and/or receiving information via the sidelink connection. The method may further comprise: receiving, from the first wireless device, a mapping between the time offset and an identity, ID, of the first wireless device. The mapping may be included in at least one of: a discovery message received by the second wireless device from the first wireless device; a sidelink establishment request message received by the second wireless device from the first wireless device. Resources used for transmitting the first information and/or the second information may be specific for the pair of the first wireless device and the second wireless device. The method may further comprise: receiving, from the first wireless device, an indication that an initial Tx beam is to be selected by the first wireless device and/or that the second wireless device shall perform the measurements. Receiving the indication may comprise receiving, from the first wireless device, at least one of the following: a Medium Access Control, MAC, Control Element, MAC CE; a MAC CE without any accompanying data; a link establishment request; a direct communication request;a PC5 signaling; a PC5-Radio Resource Control, -RRC, signaling; a layer one, LI, signaling. The LI signaling may be carried on a physical channel other than Physical Sidelink Shared Channel, PSSCH, Physical Sidelink Control Channel, PSCCH, and Physical Sidelink Feedback Channel, PSFCH.

The method may further comprise: transmitting, to the first wireless device, an indication of resources used for transmitting the second information from the second wireless device to the first wireless device. The second information and the first information may be carried on resources that are similar in at least one of a frequency and a code domain. The resources may be exclusively used by the first wireless device to transmit the first information during a first time period and exclusively used by the second wireless device to transmit the second information during a second time period differing from the first time period. The first time period and the second time period may be timely disjunct. The method may further comprise: indicating at least one of the first time period and the second time period to the first wireless device. The second time period may start upon or after at least one of the following conditions being fulfilled: the second wireless device has transmitted the second information; the second wireless device has transmitted, to the first wireless device, a Channel State Information, CSI, report; the first wireless device has selected the initial Tx beam.

The second information may be indicative of at least one of the following: a strongest measured Tx beam; a signal strength of the strongest measured Tx beam; signal strengths of all measured Tx beams that are above a predefined signal strength threshold; signal strengths of all measured Tx beams; one or more parameters for at least one of the measured Tx beams; an identity, ID, of the second wireless device. The one or more parameters may include: Rank Indicator, RI; Channel Quality Indicator, CQI; Reference Signal, RS, Resource Indicator; Reference Signal Received Power, RSRP; and/or Signal to Noise Ratio, SINR. The at least one of the measured Tx beams may correspond to the strongest measured Tx beam.

According to a fourth aspect, a second wireless device is provided. The second wireless device is configured to communicate with a first wireless device over a sidelink connection. The second wireless device is further configured to perform measurements of at least one of a plurality of transmission, Tx, beams of the first wireless device, the plurality of Tx beams transmitting first information. The second wireless device is further configured top transmit, to the first wireless device, second information indicative of at least one beam measurement result obtained by performing the measurements of the at least one of the plurality of Tx beams. The second wireless device may be configured to perform the method according to the third aspect. The second wireless device may comprise at least one processor and at least one memory, the at least one memory storing instructions which, when executed by the at least one processor, cause the at least one processor to perform the method according to the third aspect.

According to a fifth aspect, a communication system is provided. The communication system comprises the first wireless device according to the second aspect and the second wireless device according to the fourth aspect. The communication system may further comprise a base station configured to communicate with at least one of the first wireless device and the second wireless device.

According to a sixth aspect, a (e.g., non-transitory and/or computer-readable) storage medium is provided. The storage medium is storing instructions which, when executed by at least one processor of a first wireless device configured to communicate with a second wireless device over a sidelink connection, cause the first wireless device to perform the method according to any the first aspect.

According to a seventh aspect, a (e.g., non-transitory and/or computer-readable) storage medium is provided. The storage medium is storing instructions which, when executed by at least one processor of a second wireless device configured to communicate with a first wireless device over a sidelink connection, cause the second wireless device to perform the method according to the third aspect.

The term "initial beam selection" as used herein may denote a beam management procedure which the first wireless device applies to determine a Tx beam for transmissions towards the second wireless device (e.g., prior to establishment of a SL to the second wireless device). The procedure of initial beam selection may refer to a beam management and/or selection procedure which the first wireless device applies to determine a Tx beam for transmissions towards the second wireless device prior to a discovery procedure conducted in order to discover the second wireless device. The procedure of initial beam selection may refer to a beam management and/or selection procedure which the first wireless device applies to determine a Tx beam for transmissions towards the second wireless device before the first wireless device has established and/or fixed any (e.g., Tx) beam towards the second wireless device. The first wireless device may not be above to perform beam refinement (e.g., by sweeping narrower beams over a narrower range) towards the second wireless device and may then execute the initial beam selection procedure. The procedure of initial beam selection may also be triggered in other cases (e.g., if a beam failure or Radio Link Failure, RLF, has been detected by the first wireless device). The "initial beam selection" may be referred to as "initial beam pairing" or "initial beam management" or "beam selection".

SL connections may be understood as being any kind of direct connection between wireless devices, also known as D2D connections. The SL connection disclosed herein may be a Long Term Evolution (LTE) SL connection in an unlicensed carrier. Alternatively, the SL connection disclosed herein may be a New Radio (NR) SL connection. The SL connection disclosed herein may comprise or be at least one of a 5G SL connection, a connection over a millimeter-wave frequency band, a connection over a licensed or unlicensed 5G frequency band (e.g., FR2). The (e.g., first, second and/or third) wireless devices described herein may be configured as NR wireless devices. The link or radio link over which signals are transmitted between the (e.g., first, second and/or third) wireless devices may be referred to as a sidelink, or as a sidelink connection herein. Signals transmitted between the (e.g., first, second and/or third) wireless devices may be referred to as SL signals herein. The term SL may also interchangeably be called D2D link, Vehicle-to-X (V2X) link, prose link, peer-to-peer link or PC5 link. The term SL connection may also interchangeably be called D2D connection, V2X connection, prose connection, peer-to-peer connection or PC5 connection. SL signals may also interchangeably be called V2X signals, D2D signals, prose signals, peer-to-peer signals or PC5 signals.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, advantages and aspects of the present disclosure will become apparent from the following embodiments taken in conjunction with the drawings, wherein:

Fig. 1 shows a communication system in accordance with the present disclosure;

Fig. 2 shows a flowchart of a method, performed by a first wireless device, in accordance with the present disclosure;

Fig. 3 illustrates a beam sweep performed by a first wireless device;

Fig. 4 illustrates a first mapping of beams to spatial positions;

Fig. 5 illustrates a second mapping of beams to spatial positions;

Fig. 6 shows a flowchart of a method, performed by a second wireless device, in accordance with the present disclosure;

Fig. 7 illustrates an example of a set of configured resources in a frequency and time domain;

Fig. 8 illustrates an indication of resources over Tx beams.

DETAILED DESCRIPTION

In New Radio (NR), a base station (gNB) may transmit reference signals (RS) in candidate transmission (Tx) beams to determine the Tx beam to be used for DL signals. A wireless device such as a UE may perform measurements such as Layer 1 Reference Signal Received Power (Ll-RSRP) on these RSs. The RS can be a Channel State Information- (CSI-) RS for narrow beams or Synchronization Signal Block (SSB) for wide beams. The UE performing the measurements may then report the measurements to the base station. In general, an initial Tx beam selection for a DL- connection between the base station and the UE may be made for wide beams based on SSB measurements. After the initial beam selection, the gNB may refine the beam by selecting a narrow beam. To determine a new or initial Tx beam, the base station may request measurements from the UE for a set of RS resources on which the gNB can determine the strongest DL beam to the UE. Moreover, the gNB may determine its Rx beam based on the Tx beam to be used (e.g., same receive (Rx) beam for UL as is used for Tx in DL).

For the UE side, when the UE receives the DL signals, it can assume that it can use the same Rx beam as it used for receiving a previous RS. The Transmission Configuration Indicator (TCI) state may describe this association. The UE may perform measurements on a RS with a certain identifier, e.g., CSI-RS resource index or SSB/PBCH block index, and determine which beam is suitable to receive that RS. The gNB indicates, using Media Access Control (MAC) Control Element (CE) for Physical Downlink Control Channel (PDCCH) or Downlink Control Information (DCI) for Physical Downlink Shared Channel (PDSCH), which TCI state to use.

For UL transmissions, as a general rule, the UE may use beam correspondence for transmitting. In other words, the UE may use the same beam used for Rx as for Tx.

It may also happen that a UE does not support beam correspondence, as this is a UE capability. A spatial relation may be introduced between the DL RS and the UL RS and for each spatial relation, the UE may store a spatial domain filter (e.g., for a Rx beam) of the source DL RS and apply the same spatial domain filter (e.g., for a Tx beam) for every transmission of the target UL RS.

If the UE does not support beam correspondence, Sounding Reference Signal (SRS) sweeping may be used. In this case, multiple SRS resources may be transmitted to the gNB and configured with a spatial relation. These SRS resources can be transmitted using spatial domain filters. The gNB may measure the values in the SRS and indicate to the UE by means of Radio Resource Control (RRC) or MAC-CE which spatial relation to be used for data transmission.

The Third Generation Partnership Program (3GPP) specified the Long Term Evolution (LTE) Device-to-Device (D2D) technology, also known as sidelink (SL) or the PC5 interface, as part of Release 12 (Rel-12). Support was enhanced during Rel-13. In Rel-14, the LTE sidelink was extensively redesigned to support vehicular communications, commonly referred to as Vehicle-to-X (V2X) or Vehicle-to-Vehicle (V2V). Support was again enhanced during Rel-15. From the point of view of the lowest radio layers, the LTE SL uses broadcast communication. That is, transmission from a UE targets any receiver that is in range. In Rel-16, 3GPP introduced sidelink for the 5G new radio (NR), details of which are described 3GPP Technical Specification (TS) 38.321 and TS 38.331. The driving use case was vehicular communications with more stringent requirements than those typically served using the LTE SL.

To meet these requirements, the NR SL should be capable of broadcast, groupcast, and unicast communications. In groupcast communication, the intended receivers of a message are typically a subset of the wireless devices (e.g., vehicles) near the transmitter, whereas in unicast communication, there is a single intended receiver. Hybrid Automatic Repeat Request (HARQ) feedback based retransmission may be supported for unicast and groupcast.

NR SL may use 2 stage Sidelink Control Information (SCI), the 1st stage SCI being transmitted on the Physical Sidelink Control Channel (PSCCH) and used for the scheduling of the Physical Sidelink Shared Channel (PSSCH), and the 2nd stage SCI on PSSCH. PSCCH carrying 1st stage SCI and the PSSCH scheduled by the 1st stage SCI may be transmitted in the same slot but in different symbols.

NR sidelink transmissions may have the following two modes of resource allocations:

• Mode 1: Sidelink resources are scheduled by the gNB, including both dynamic scheduling and configured grant.

• Mode 2: The UE autonomously selects sidelink resources from a (pre-) configured sidelink resource pool(s) based on the channel sensing mechanism.

For RRC CONNECTED UE, a UE may be configured to adopt either Mode 1 or Mode 2 resource allocation (RA). In other cases, only Mode 2 may be adopted.

In recent 3GPP meetings, sidelink evolution in general has been discussed (see e.g., 3GPP documents Rl-1903075, RP-213678 and RP-222806). One topic to be studied for the frequency range 2 (FR2) is initial beam selection and PC5 link establishment. The initial beam selection may be done among available wide-beams, followed by a beam refinement where a narrow-beam may be selected. When performing beam selection, beam sweeping may need to be done at both the transmitting and receiving side and efficient schemes for this may need to be defined.

In Uu, the gNB may broadcast SSB and/or Physical Broadcast Channel (PBCH) blocks beamformed at different directions in the cell. A UE in RRC IDLE would need to perform the initial beam selection and set up its RRC Connection using the selected initial beam, which is typically a wide beam. The UE in RRC IDLE may measure the SSB/PBCH blocks periodically and select the RX beam whose associated SSB/PBCH block resources have the strongest RSRP. In order to select the RX beam, the UE may be configured with a RSRP threshold. The UE may then only select the SSB beams whose measured RSRP above the threshold.

As soon as the UE selects the SSB and/or PBCH, the UE may use the Random Access Channel (RACH) resources (i.e., RACH occasions and preambles) associated with the SSB/PBCH to initiate a RACH procedure. After the RACH procedure, the gNB may configure the UE with a TCI state indicating the RX beam that the UE shall use for subsequent PDSCH reception and PUSCH transmission.

In SL, the procedure of initial beam selection may be defined prior to establishment of a unicast link. The existing Uu procedure thus may not be directly reused for SL due to the following issues:

1) A SL link involves at least two UEs. An initial beam may need to be determined involving both UEs, so that they can apply corresponding TX beam and RX beam pointing to the determined beam direction. While only the behaviour of a single UE is defined in the Uu procedure, for SL, the procedures and the behaviors for both UEs need to be considered.

2) In Uu, the gNB signals PRACH and SSB configurations in the SIB. Therefore, both the gNB and each UE in the cell have a common understanding on the resources in frequency and time, based on which a UE can initiate the procedure to select an initial beam. Both the gNB and the UE are synced in terms of the procedure of initial beam selection. However, such a procedure may be missing in SL.

Fig. 1 shows a communication system 100 in accordance with the present disclosure. The system 100 comprises a first wireless device UE1 and a second wireless device UE2 that are configured to communicate with one another over a sidelink (SL) connection. Each of the wireless devices comprises at least one processor 2 communicatively coupled to at least one memory 4 and at least one antenna system 6. The at least one memory stores instructions causing the at least one processor 2 to perform the method described herein for the respective UE. The respective UE may transmit information over Tx beams via its antenna system 6, and receive information over Rx beams via its antenna system 6. The system 100 may further comprise a base station 8 such as a gNB, configured to communicate with one or more of the UEs. A third wireless device UE3 may be also be comprised in the system 100 and configured to communicate with at least one of UE1, UE2 and base station 8.

Fig. 2 shows a method, performed by a first wireless device (e.g., UE1), in accordance with the present disclosure. The method comprises a step 202 of transmitting first information over a plurality of transmission, Tx, beams. The method comprises a step 204 of receiving, from the second wireless device (e.g., UE2), second information indicative of at least one beam measurement result for at least one of the Tx beams. The method comprises a step 206 of selecting, based on the second information, one of the plurality of Tx beams as an initial Tx beam to be used by the first wireless device (e.g., UE1) for the sidelink connection.

The technique may be described herein from a REQUESTING UE (e.g., UE1) and REPORTING UE (e.g., UE2) point of view. A SL UE (e.g., UE1) and, if the UE is in network (NW) coverage, its serving gNB (e.g., gNB 8), may operate with a same radio access technology (RAT) such as NR or LTE. Alternatively, other combinations of RATs between the SL UE and its serving gNB may be used. If the present disclosure refers to "a UE configures" or "configured by a UE", this may mean that the UE determines the configuration by itself or its serving gNB determines the configuration and informs it to the UE. The technique disclosed herein may be applicable to SL UEs with beamforming based SL transmission or reception with any cast type including unicast, groupcast or broadcast. The technique disclosed herein may be described in the context of a UE pair, e.g., UE1 and UE2 which are involved in a SL unicast transmission. It may be assumed that the TX UE determines the TX beam in one direction. For example, for the direction from UE1 to UE2, UE1 may determine its TX beam based on beam measurement results provided by UE2 (e.g., SL CSI reporting). Vice versa, for the direction from UE2 to UE1, UE2 may determine its TX beam based on beam measurement results provided by UE1 (e.g., SL CSI reporting). The present disclosure is not limited by this assumption and equally applicable in case other options on how to determine the TX beam are adopted. For example, a beam correspondence may be configured for UE1 or UE2 between a RX beam on one direction and a TX beam on the other direction. In this way, whenever the UE has determined a RX beam on one direction, the UE may determine a TX beam on the other direction according to the beam correspondence. In this manner, the UE may transmit in the direction from which it received transmissions. Generally speaking, the UE1 may perform the below steps in the method for initial beam selection: iterate the transmission using different TX beams among a set of beams at different time instants (e.g., step 202); monitor response from UE2 indicating one or multiple preferred beams from UE2 perspective (e.g., step 204); and select the beam according to the response received from UE2 (e.g., step 206).

For a UE (e.g., UE1 operating as a TX UE) capable of beamforming based SL transmission or reception on a SL carrier, the UE may be triggered to sweep its TX beam towards at least a neighbor UE (e.g., UE2 operating as a RX UE) on the SL carrier when at least one of the following conditions is met: (1) UE1 has new data arrival towards UE2 (e.g., the L2 destination which is associated with UE2); (2) UE1 determines that UE2 may be capable of beamforming based SL transmission and reception; (3) link establishment towards UE2 needs to be performed.

In a first variant, the determination in (2) is based on information that the intended SL transmission and/or reception will be carried out in a SL carrier (e.g., the SL carrier is in FR2) where beamforming needs to be supported. Such information may be configured or preconfigured to UE1. As an alternative, such information may be configured to UE1 by the gNB. In a second variant, the determination in (2) is b based on the information obtained in previous communications with UE2. In a third variant, the determination in (2) is based on the information on UE2's capabilities which indicates that UE2 supports beamforming based SL transmission and/or reception in the concerned carriers. UE2 may signal this information to UE1. The link establishment in (3) may be triggered by UE1 itself or upon reception of a request message from UE2.

The beam sweep may mean that UE1 uses different TX beams to perform transmissions on the concerned SL carrier towards UE2. This is schematically illustrated in Fig. 3. For each transmission, also referred to as a beam initialization signaling herein, the receiving UE2 may deduce the following information: the index of the beam on which the transmission is carried; the ID of the UE which performs the transmission.

Each transmission may be initiated by UE1 using at least one of the following resources or signals: SL-SSB/PBCH; SL-CSI RS; any other types of SL RS; SL resources carrying PSSCH transmission; SL resources carrying PSCCH transmission. UE1 may select the sources among the set of configured resources considering its UE ID and/or the UE ID of the peer UE (e.g., UE2). In this way, UEs who performing the initial beam selection at the same time can avoid using the same resources. In an example, UE1 determines the index of a resource by a mathematic formula using its UE ID and/or the UE ID of the peer UE (e.g., UE2) as inputs. In another example, UE1 may select a resource randomly among the set of configured resources.

Each transmission may be expressed as a LI control signaling, MAC CE or an upper control signaling (e.g., PC5-RRC signaling, PC5-S signaling or discovery signaling) indicating at least one of the beam index and the ID of UE1.

When UE1 iterates the transmission using different beams at different time instants, the beam index contained in the transmission/signaling may also change correspondingly while the UE ID remains the same.

The UE1 may determine a set of Tx beams considering UE2's location. The location information of UE2 can be obtained by UE1 via at least one of the following alternatives: (a) derived based on knowledge of previous transmission or reception from UE2; (b) UE2's location information is received from the gNB or another neighbor UE. In alternative (a), the knowledge may include what TX or RX beam was used in a previous transmission or reception from UE2. In alternative (a), the knowledge may include location information obtained in a previous transmission or reception from UE2.

UE2's location information may comprise at least one of the following: UE2's GNSS location; ID of the cell or the gNB serving UE2; positioning measurement results such as TDOA, Multi-RTT, AoD, AoA.

An AI/ML module implemented in UE1 may predict UE2's location based on information including such as previous UE location, UE2's velocity, UE2's other information such as UE2's daily routine etc.

Based on trigger conditions as described above, UE1 may start a cycle or a window to sweep TX beams towards UE2. A cycle or window may be configured with multiple transmission positions, where each position may be mapped to a TX beam. Each position may be associated with a position index, which may be different from the index of the TX beam which is mapped to the position. Each position may span in time a number of OFDM symbols or slots. As shown in Fig. 4, if each position is mapped to a different TX beam, the index of a position may be the same as the index of the TX beam mapped to the position. In an alternative variant illustrated in Fig. 5, multiple positions (e.g., consecutive in time) are mapped to the same TX beam. In this variant, the indices of the positions are different from the index of the TX beam associated with the positions. In the variant of Fig. 3, UE1 can repeat the same TX beam towards UE2 several times. In a still further variant (not shown), multiple beams may map to the same position. In this case, the transmission on each different beam may use different frequency resources. This may require UE to support multi-beam transmissions (e.g., performing transmissions using multiple beams simultaneously).

The index of a position in a window may be defined relative to the start time of the window or cycle. UE1 may indicate the start time of a window or cycle to UE2, e.g., the first SL-SSB or CSI-RS transmitted in the window or cycle may be in a specific SL- SSB or CSI-RS resource or using specific SL-SSB or CSI-RS sequence, or one bit may be introduced in SCI, MAC CE or MAC PDU header where "1" (or "0") indicates it is the first transmission in a window or cycle. Such indication may also indicate that UE1 starts to perform Tx beam sweep and needs response from UE2. UE2 may then respond to UE1 whether a transmission from UE1 in the Nth position within a window or cycle has a quality above a configurable threshold.

The (e.g., maximum) length or (e.g., maximum) number of transmissions in a window or cycle may be (e.g., pre-) configured. If UE2 does not receive an indication indicating that a new window or cycle is or will be started, it may stop to send the response to UE1 after the end of the current window or cycle. Alternatively, UE1 may explicitly indicate the end of a window or cycle using methods similar as indicating start of a window or cycle as described above.

The mapping between the positions and the Tx beams may be (e.g., pre-) configured (e.g., in advance) or dynamically changed by UE1 and different in each window or cycle. UE1 may skip some positions during a window. This may occur when UE1 already received a response from UE2 indicating quality report of beams.

As one option, a time offset compared to the normal (e.g., SL-SSB) transmissions is used to define new (e.g., SL-SSB) resources (e.g., same frequency/PRBs) and configured during the initial link establishment. In this way, the time and frequency resources defined by the time offset may be used only by the two UEs involved in the initial beam selection. The mapping between the time offsets and the L2 IDs of the transmitting UE may be included in the discovery message or link establishment request message. In this way, a UE receiving the transmissions from another UE may determine the other UE's ID directly, without reading further signaling from the other UE in order to identify the UE ID of the other UE.

In another option, separate resources (e.g., SL-SSB) compared to the resources used for non-initial beam selection based SL transmission and/or reception are configured for initial beam selection. Based on the resources where SL transmission/reception occurs, each UE understands the purpose of the detected SL transmission and/or reception.

During a window the number of positions mapped to a beam may be different from the number of positions mapped to another beam. Such flexibility may be beneficial for example when UE1 intends to repeat different times at a certain direction compared to another direction.

UE1 may start a window or cycle for TX beam sweep periodically or based on events. In the former, UE1 and UE2 may have a common understanding on when to perform or monitor potential beam sweep. For the latter, UE1 may start a TX beam sweep at a time instant which may be unknown to UE2. UE1 may thus repeat windows a couple of times until UE2 has detected the beam sweep.

UE1 may initiate a beam initialization signaling using a MAC CE. In this case, UE1 may transmit the MAC CE alone without any accompanying data.

A beam initialization signaling may be carried or expressed as a PC5-S signaling (e.g., link establishment request or direct communication request), a discovery signaling or a PC5-RRC signaling.

A beam initialization signaling may be a LI signaling carried on a new or separate physical channels other than PSSCH, PSCCH, PSFCH.

A beam initialization signaling may be carried by a SL-SSB/PBCH transmission. From the SL-SSB/PBCH transmission, the receiving UE (e.g., UE2) may determine the beam and the transmitting UE (e.g., UE1). The options for determining the identity of the transmitting UE (UE1) can be one of the following:

(Option A) UE identity is part of the MIB (PBCH). The UE identity may be the L2 ID of the transmitting UE or a local ID mapped to the L2 ID. The mapping may be configured/preconfigured to UE. Alternatively, the mapping may be included in the discovery message or link establishment request message.

(Option B) The UE identity is derived from a mapping from SLSS ID to the L2 ID where the SLSS ID is assigned or selected during the initial L2 link establishment. The mapping may be configured/preconfigured to UE. Alternatively, the mapping may be included in the discovery message or link establishment request message. When the SLSS ID is assigned during link establishment, this means that the UE may not change SLSS ID during the beam selection procedure. Such SLSS ID may reuse integer values in the range between 336 and 671, which is typically used for synchronization purpose by a SyncRef UE which is out of GNSS/gNB coverage or two or more hops away from GNSS/gNB.

The resources may be used by both UE1 and UE2 for initial beam selection for transmission in both directions between the UEs. For instance, UE1 may first transmit a beam initialization signaling as described above, UE2 that receives the signaling may confirm in a discovery response or a link establishment acknowledgement message whether it will also use the same resources for initial beam selection for transmitting to UE1. A scheme could be configured which determines which of and/or how the UEs (e.g., UE1 or UE2) can use the same resources for initial beam selection. In a first option, UE1 can use the resources for a time period 1 and then UE2 can use the same resources for a time period 2. The time period may be indicated in SL-MIB or in a discovery or link establishment request/acknowledgement message. In a second option, UE1 starts to use the resources and signals to UE2 when UE2 can start to use them. The UE2 may start using the resources after it has sent a CSI report to UE1 that UE1 uses for initial beam selection.

Fig. 6 shows a method, performed by a second wireless device (e.g., UE2), in accordance with the present disclosure. The method comprises a step 602 of performing measurements of at least one of a plurality of transmission, Tx, beams of the first wireless device (e.g., UE1), the plurality of Tx beams transmitting first information. The method comprises a step 604 of transmitting, to the first wireless device (e.g., UE1), second information indicative of at least one beam measurement result obtained by performing the measurements of the at least one of the plurality of Tx beams.

The second wireless device UE2 may be referred to as receiving UE. UE2, after measuring the beams of the transmitting wireless device UE1, may respond to UE1 with a report message. The report may contain at least one of: an indication of the strongest beam(s); an indication of signal strengths of the beams with signal strength above a threshold; an indication of signal strengths of all beams; RI, CQI, RS Resource Indicator, RSRP, SINR, etc. for the selected beams; the reporting UEs ID.

A set of configured resources may be configured or preconfigured to UE2. Each configured resource (CR) spans x PRBs or sub carriers or sub channels in frequency and y OFDM symbols or slots in time. Each CR may be used by the receiving UE (e.g., UE2) to transmit the report message to UE. As a non-limiting example illustrated in Fig. 7, the set of CRs may be indexed and sorted as follows:

• First, in increasing order of frequency resource indexes for frequency multiplexed CRs

• Second, in increasing order of time resource indexes for time multiplexed CRs (e.g., assuming a slot may contain multiple CR occasions in time).

• Third, in increasing order of indexes for slots.

A slot in the time domain to may cover multiple CR occasions in time. A slot may be equal to a normal slot, or z OFDM symbols in time. The UE may be configured or preconfigured with a fixed number of CRs in frequency.

CR occasions may have the same or different time durations. CRs may be consecutively or non-consecutively distributed in frequency and in time.

The set of CRs may be common to all UEs or a set of UEs in the proximity (e.g., UE1, UE2 and UE3). There may multiple sets of CRs configured or preconfigured in the proximity.

A set of CRs may be associated with one or multiple L2 Destination ID. In this way, each concerned UE knows the resources which need to be monitored by the UE for reception of potential report messages.

The index of a CR may be included in a beam initialization signaling (e.g., sent by UE1). Upon reception of a beam initialization signaling from UE1 on a beam (e.g., the strongest receiving beam), UE2 can use this CR to transmit the report message indicating the strongest beam which is measured by UE2. If there are multiple beams measured above a configured threshold, UE2 may determine to send the report message on (e.g., a part of or) all the CRs which are indicated in the beam initialization signaling received on these strongest beams. When the report message is transmitted multiple times, it can increase the likelihood that UE1 can receive it successfully.

This means that when UE1 determines to send a beam initialization signaling, UE1 may also needs to determine a corresponding CR for each TX beam, as indicated in Fig. 8. In this way, upon reception of the report message, UE1 may directly derive strongest beam from UE2 perspective based on the resource in which the report is received.

In one option, UE1 uses a CR according to the gNB's (e.g., base station 8) decision. In this option, UE1 may need to send a request message to the gNB for requesting a CR for a TX beam. Upon reception of the request message, the gNB may allocate a CR among the sets of CRs for UE1.

In one option, UE1 selects a CR by itself (e.g., randomly) among the sets of CRs.

In one option, UE1 selects the CR with the index determined based on the ID of UE1, the ID of UE2, and the index of the corresponding TX beam. A formula may be defined for determining the index CRI of the CR. As described above, the ID of a UE in the formula may be a L2 Destination ID, a local ID (e.g., calculated based on the L2 Destination ID) or any other ID. In an example, the formula may be expressed as

CRI = F(UE1_ID, UE2_ID, beam index)mod(N)

Where N denotes the total number of CRs, F() may be any mathematical function. The function may be defined in such a way that the outputted index CRI of a selected CR is unique for different TX beams belonging to the same and different TX UEs in the proximity.

The UE2 may have two options to determine a TX beam for transmitting the report message to UE1. According to a first option, the UE2 performs a TX beam sweep towards UE1, similar to the procedure described above for UE1. According to a second option, UE2 determines a TX beam corresponding to the strongest RX beam. In other words, UE2 may support beam correspondence. UE2 can then transmit in the direction from which it received transmissions from UE1.

The time occasions for UE2 to monitor potential beam sweep from UE1 or any other neighbor UE, and the time occasion for UE2 to provide a report message to the corresponding TX UE may be separated in time so that they are not overlapping, for example when UE2 cannot perform monitoring and transmission simultaneously.

The responding UE (e.g., UE2) may send a report message as described above to the UE1 when the entire beam sweep has been received. If several beam sweeps are conducted the report may be sent after each beam sweep. Alternatively, the responding UE (e.g., UE2) may send a report message as described above to the UE1 after each beam is received. For example, the receiving UE reports when it receives a beam with a defined quality (e.g., a RSRP above a configured threshold).

The UE1 may select the beam according to the report received from UE2, as described above.

Configurations may be configured/preconfigured to UE in the proximity. Configurations may be configured by the gNB via system information, master information, RRC signaling, MAC CE or LI signaling. Configurations may be associated with one or multiple IDs which are known to all UEs (e.g., L2 Destination IDs). Configurations may comprise at least one of the following information: information on resources which can be used by a UE for transmitting a beam initialization signaling and/or for performing a TX beam sweep; information on resources which can be used by a UE for transmitting a report message comprising beam measurement results to its peer UE; information on any other configuration which is relevant to any one of the above aspects, embodiments, examples, alternatives, variants and options (e.g., any threshold or timer setting in the initial beam selection procedure).

The initial beam selection may be started by a UE (e.g., UE1) at different time points. In a first variant, the initial beam selection is started at the beginning of a link establishment. In this case the link establishment request message may be transmitted multiple times in a beam sweep manner, each of the MAC PDU (e.g., corresponding to each transmission) containing the message or the associated SCI may include an index associated with the used beam. The receiving UE (e.g., UE2) receiving the message could indicate in the MAC PDU containing the link establishment acknowledgement message or the associated SCI the index of the received beam which has the best quality. In this case, it may not be necessary to explicitly include the UE ID in the link establishment message as the UE ID is already indicated in the SCI or MAC header. In a second variant, the initial beam selection is started after initial link establishment. In this case the link establishment request or acknowledgement message is transmitted (e.g., once) without beamforming. After the initial link establishment acknowledgement is received by UE1, UE1 may start the initial beam selection.

It is to be understood that for any one of the above methods and examples, either UE1 or UE2 can operate as a TX UE or a RX UE or both at the same time. In an example, UE1 works as the TX UE for the direction from UE1 to UE2, UE1 may determine the TX beam for the direction from UE1 to UE2 based on reports provided by UE2. Meanwhile, UE1 operates as the RX UE for the direction from UE2 to UE1. UE1 measures the RS resources configured for the initial beam selection and provides a report to UE2 for the direction from UE2 to UE1. Therefore, any one of the above methods and examples is applicable to both UE1 and UE2.

The present disclosure also provides for the following examples:

1. A method performed by a first wireless device (UE1) configured to communicate with a second wireless device (UE2) over a sidelink connection, the method comprising: transmitting (202) first information over a plurality of transmission, Tx, beams; receiving (204), from the second wireless device (UE2), second information indicative of at least one beam measurement result for at least one of the Tx beams; and selecting (206), based on the second information, one of the plurality of Tx beams as an initial Tx beam to be used by the first wireless device (UE1) for the sidelink connection.

2. The method of example 1, further comprising, after having selected the initial Tx beam, at least one of the following steps: establishing the sidelink connection between the first wireless device (UE1) and the second wireless device (UE2); transmitting data via the initial Tx beam to the second wireless device (UE2).

3. The method of example 1 or 2, wherein the step of transmitting the first information is triggered when at least one of the following conditions is met: the first wireless device (UE1) receives data to be transmitted towards the second wireless device (UE2); the first wireless device (UE1) determines that the second wireless device (UE2) is configured to receive and/or transmit information over a sidelink connection; a sidelink connection needs to be established between the first wireless device (UE1) and the second wireless device (UE2); the first wireless device receives a request from the second wireless device (UE2) to select an initial Tx beam and/or establish a sidelink connection between the first wireless device (UE1) and the second wireless device (UE2); a link establishment procedure for establishing a sidelink connection between the first wireless device (UE1) and the second wireless device (UE2) is started; the first wireless device (UE1) receives a link establishment acknowledgement from the second wireless device (UE2).

4. The method of example 3, wherein the first wireless device (UE1) determines that the second wireless device (UE2) is configured to receive and/or transmit information over a sidelink connection based on at least one of the following: requirement information indicating that a sidelink transmission and/or reception needs to be performed using a sidelink carrier requiring beamforming; capability information obtained from the second wireless device (UE2).

5. The method of example 4, wherein the requirement information is preconfigured at the first wireless device (UE1) or configured by a base station.

6. The method of example 5, further comprising: receiving the requirement information from the base station.

7. The method of any one of examples 4 to 6, wherein the capability information indicates that the second wireless device (UE2) supports beamforming based sidelink transmission and/or reception.

8. The method of any one of examples 1 to 7, wherein the first information is beam-specific.

9. The method of any one of examples 1 to 8, wherein the first information transmitted over the plurality of Tx beams differs between at least two of the Tx beams.

10. The method of any one of examples 1 to 9, wherein the first information is indicative of the respective Tx beam and/or indicative of an index or identifier of the respective Tx beam. 11. The method of any one of examples 1 to 10, wherein the first information is indicative of an identity, ID, of the first wireless device (UE1).

12. The method of example 11, wherein the ID of the first wireless device (UE1) is included in the first information or derivable from the first information.

13. The method of example 11 or 12, wherein the ID of the first wireless device (UE1) is a layer two, L2, ID of the first wireless device (UE1) or a local ID associated with a layer two, L2, ID of the first wireless device (UE1).

14. The method of any one of examples 11 to 13, wherein the ID of the first wireless device (UE1) is derivable from the first information using a mapping between the ID of the first wireless device (UE1) and at least a portion of the first information.

15. The method of any one of examples 11 to 13, wherein the ID of the first wireless device (UE1) is a local ID associated by a mapping to a layer two, L2, ID of the first wireless device (UE1).

16. The method of example 14 or 15, wherein the mapping is a mapping is between a layer two, L2, ID of the first wireless device (UE1) and a Sidelink Synchronization Signal Identity, SLSS ID.

17. The method of example 16, wherein the SLSS ID is assigned or selected during an initial L2 link establishment.

18. The method of any one of examples 14 to 17, wherein the mapping is preconfigured.

19. The method of any one of examples example 14 to 18, further comprising: transmitting the mapping or information indicative of the mapping to the second wireless device (UE2).

20. The method of example 19, wherein the mapping or the information indicative of the mapping is transmitted in a discovery message or in a link establishment request message.

21. The method of any one of examples 11 to 20, wherein the ID of the first wireless device (UE1) is part of a Master Information Block, MIB.

22. The method of any one of examples 1 to 21, wherein at least one of the first information and the second information is carried by one or more of the following resources or signals:

Medium Access Control, MAC, Control Element, MAC CE;

Sidelink Control Information, SCI;

Sidelink Synchronization Signal Block, SL-SSB;

Physical Broadcast Channel, PBCH; a Sidelink Reference Signal, SL RS, such as a Sidelink Channel State Information-Reference Signal, SL CSI-RS; one or more sidelink resources carrying a Physical Sidelink Shared Channel, PSSCH, transmission; one or more sidelink resources carrying a Physical Sidelink Control Channel, PSCCH, transmission.

23. The method of any one of examples 1 to 22, wherein one or more resources for transmitting the first information are selected from a set of configured resources.

24. The method of example 23, wherein the one or more resources are selected based on an identity, ID, of the first wireless device (UE1) and/or an identity, ID, of the second wireless device (UE2).

25. The method of example 23 or 24, wherein each of the configured resources has an associated resource index, and the one or more resources are selected based on the associated resource index or indices.

26. The method of example 25, wherein the associated index or indices are determined as result(s) of a formula using the identity, ID, of the first wireless device (UE1) and/or the identity of the second wireless device (UE2) as input parameter(s). 27. The method of example 23, wherein the one or more resources are randomly selected from the set of configured resources.

28. The method of any one of examples 23 to 27, wherein the one or more resources are selected by the first wireless device (UE1).

29. The method of any one of examples 23 to 27, wherein the one or more resources are selected by a base station.

30. The method of example 29, further comprising: receiving, from the base station, an indication of the selected one or more resources.

31. The method of example 29 or 30, further comprising: transmitting, to the base station, a request for a selection of one or more configured resources.

32. The method of any one of examples 23 to 31, wherein the set of configured resources are configured by a base station.

33. The method of example 32, further comprising: receiving, from the base station, an indication of the set of configured resources.

34. The method of example 33, wherein the set of configured resources is indicated by at least one of the following: system information; master information;

Radio Resource Control, RRC, signaling;

MAC CE; layer one, LI, signaling.

35. The method of any one of examples 32 to 34, further comprising: transmitting, to the base station, a request for configuring the set of configured resources.

36. The method of any one of examples 1 to 35, wherein the plurality of Tx beams are determined based on a location of the second wireless device (UE2).

37. The method of example 36, wherein the plurality of Tx beams are determined by the first wireless device (UE1).

38. The method of any one of examples 1 to 37, wherein the initial Tx beam is selected based on a location of the second wireless device (UE2).

39. The method of any one of examples 36 to 38, wherein the location of the second wireless device (UE2) is obtained based on at least one of the following: a Tx beam previously used by the first wireless device (UE1) in a transmission to the second wireless device (UE2); a reception, Rx, beam previously used by the first wireless device (UE1) in a reception from the second wireless device (UE2); location information.

40. The method of example 39, wherein the location information is indicative of at least one of the following: a previous location of the second wireless device (UE2); a current or previous movement velocity of the second wireless device (UE2); a current or previous movement path of the second wireless device

(UE2); information indicative of a regular behavior of the second wireless device (UE2).

41. The method of example 39 or 40, wherein the location information is indicative of or based on a prediction of the location of the second wireless device (UE2).

42. The method of example 41, wherein the prediction of the location of the second wireless device (UE2) is based on at least one of the following: a previous location of the second wireless device (UE2); a current or previous movement velocity of the second wireless device (UE2); a current or previous movement path of the second wireless device (UE2); information indicative of a regular behavior of the second wireless device (UE2).

43. The method of example 41 or 42, wherein the prediction is determined by an artificial intelligence module and/or a trained machine learning model.

44. The method of any one of examples 39 to 43, wherein the location information is obtained by the first wireless device (UE1) from at least one of the following entities: the second wireless device (UE2); a third wireless device (UE3); a base station.

45. The method of any one of examples 39 to 44, wherein the location information comprises at least one of the following: a position of the second wireless device (UE2) determined using a global navigation satellite system, GNSS; an identity, ID, of a cell serving the second wireless device (UE2); an identity, ID, of a base station serving the second wireless device (UE2); one or more position measurement results.

46. The method of example 45, wherein the one or more position measurement results comprise at least one of the following: a Time Difference of Arrical, TDOA; a Round Trip Time, RTT; a Multi-Round Trip Time, Multi-RTT; an Angle of departure, AoD; an Angle of Arrival, AoA.

47. The method of any one of examples 1 to 46, wherein the second information is received on one or more resources associated with one of the plurality of Tx beams, and the one of the plurality of Tx beams is selected as the initial Tx beam. 48. The method of any one of examples 1 to 47, wherein the plurality of Tx beams consists of multiple subsets of Tx beams and the first wireless device (UE1) transmits the first information over one subset of Tx beams at a time.

49. The method of any one of examples 1 to 48, wherein the first wireless device (UE1) transmits the first information over different Tx beams of the plurality of Tx beams at different time instants.

50. The method of any one of examples 1 to 49, wherein the first wireless device (UE1) transmits the first information over the plurality of Tx beams by transmitting the first information over one Tx beam at a time.

51. The method of any one of examples 1 to 50, wherein the first wireless device (UE1) performs beam sweeping to transmit the first information over the plurality of Tx beams.

52. The method of any one of examples 1 to 51, wherein each of two or more of the plurality of Tx beams extends into a beam-specific spatial direction.

53. The method of any one of examples 1 to 52, wherein each of the plurality of Tx beams extends into a beam-specific spatial direction.

54. The method of any one of examples 1 to 53, wherein the first information is transmitted such that the first information is provided to different spatial positions.

55. The method of example 54, wherein the first information is transmitted such that the first information is provided to the different spatial positions at different times.

56. The method of example 54 or 55, wherein each of the different spatial positions is associated with at least one of the plurality of Tx beams.

57. The method of any one of examples 54 to 56, wherein at least two of the different spatial positions are associated with a same one of the plurality of Tx beams.

58. The method of example 57, wherein the first information is transmitted to the at least two of the different spatial positions using different frequency resources.

59. The method of any one of examples 54 to 58, wherein at least two of the different spatial positions are associated with different ones of the plurality of Tx beams.

60. The method of any one of examples 54 to 59, wherein an association between the plurality Tx beams and the spatial positions is preconfigured.

61. The method of any one of examples 54 to 59, wherein an association between the plurality of Tx beams and the spatial positions is determined and/or dynamically adapted by the first wireless device (UE1).

62. The method of any one of examples 54 to 61, wherein the first information is transmitted for one or more of the spatial positions over a plurality of slots or Orthogonal Frequency-Division Multiplexing, OFDM, symbols.

63. The method of any one of examples 1 to 62, wherein the first information is transmitted within a time window.

64. The method of example 63, further comprising: indicating, to the second wireless device (UE2), at least one temporal location associated with the time window.

65. The method of example 64, wherein the at least one temporal location comprises one or more of: a start time of the time window; a halftime of the time window; an end time of the time window.

66. The method of example 64 or 65, wherein the first wireless device (UE1) indicates the at least one temporal location associated with the time window by transmitting, to the second wireless device (UE2), a first SL-SSB or CSI-RS in a SL-SSB or CSI-RS resource associated with the at least one temporal location.

67. The method of example 64 or 65, wherein the first wireless device (UE1) indicates the at least one temporal location associated with the time window by transmitting, to the second wireless device (UE2), a first SL-SSB or CSI-RS using a SL-SSB or CSI-RS sequence associated with the at least one temporal location.

68. The method of example 64 or 65, wherein the first wireless device (UE1) indicates the at least one temporal location associated with the time window by transmitting a message to the second wireless device (UE2), the message including a bit or flag indicative of the at least one temporal location.

69. The method of example 68, wherein the message comprises one or more of:

Sidelink Control Information, SCI;

Medium Access Control, MAC, Control Element, MAC CE;

Medium Access Control Protocol Data Unit, MAC PDU, header.

70. The method of any one of examples 63 to 69, wherein a length of the time window and/or a number of emissions in the time window is preconfigured.

71. The method of any one of examples 63 to 70, wherein the time window, including the emission of the first information, is repeated at least twice.

72. The method of example 71, wherein the time window, including the emission of the first information, is repeated periodically.

73. The method of any one of examples 1 to 72, wherein resources used for transmitting the first information and/or the second information differ from other resources that fulfil at least one of the following criteria: the other resources are used in a sidelink connection of the first wireless device (UE1); the other resources are used in a sidelink connection of the second wireless device (UE2); the other resources are used in a selection of a non-initial beam.

74. The method of example 73, wherein the resources used for transmitting the first information and/or the second information differ from the other resources in at least one of a time domain and a spatial domain.

75. The method of example 73 or 74, wherein transmission time points used for transmitting the first information and/or the second information differ, by a time offset, from transmission time points used for transmitting and/or receiving information via the sidelink connection.

76. The method of example 74, further comprising: indicating, to the second wireless device (UE2), a mapping between the time offset and an identity, ID, of the first wireless device (UE1).

77. The method of example 76, wherein the mapping is included in at least one of: a discovery message transmitted to the second wireless device (UE2) from the first wireless device (UE1); a sidelink establishment request message transmitted to the second wireless device (UE2) from the first wireless device (UE1).

78. The method of any one of examples 1 to 77, wherein resources used for transmitting the first information and/or the second information are specific for the pair of the first wireless device (UE1) and the second wireless device (UE2).

79. The method of any one of examples 1 to 78, wherein the first information is transmitted using the same resources as used for receiving the second information.

80. The method of example 79, wherein the same resources are exclusively used by the first wireless device (UE1) during a first time period and exclusively used by the second wireless device (UE2) during a second time period differing from the first time period.

81. The method of example 80, wherein the first time period and the second time period are timely disjunct.

82. The method of example 80 or 81, further comprising: indicating at least one of the first time period and the second time period to the second wireless device (UE2).

83. The method of any one of examples 80 to 82, wherein the at least one of the first time period and the second time period is indicated in one or more of the following: a Sidelink Master Information Block, SL-MIB; a discovery request; a link establishment request; an acknowledgement message.

84. The method of any one of examples 80 to 83, wherein the second time period starts upon or after at least one of the following conditions being fulfilled: the first wireless device (UE1) has received the second information; the first wireless device (UE1) has received, from the second wireless device (UE2), a Channel State Information, CSI, report; the first wireless device (UE1) has selected the initial Tx beam.

85. The method of any one of examples 1 to 84, further comprising: transmitting an indication to the second wireless device (UE2) that an initial Tx beam is to be selected by the first wireless device (UE1) and/or that measurements of the Tx beams are to be performed by the second wireless device (UE2).

86. The method of example 85, wherein transmitting the indication comprises transmitting, to the second wireless device (UE2), at least one of the following: a Medium Access Control, MAC, Control Element, MAC CE; a MAC CE without any accompanying data; a link establishment request; a direct communication request; a PC5 signaling; a PC5-Radio Resource Control, -RRC, signaling; a layer one, LI, signaling.

87. The method of example 86, wherein the LI signaling is carried on a physical channel other than Physical Sidelink Shared Channel, PSSCH, Physical Sidelink Control Channel, PSCCH, and Physical Sidelink Feedback Channel, PSFCH.

88. The method of any one of examples 1 to 87, wherein receiving the second information triggers selecting the initial Tx beam.

89. A first wireless device (UE1) configured to communicate with a second wireless device (UE2) over a sidelink connection, the first wireless device being further configured to: transmit (202) first information over a plurality of transmission, Tx, beams; receive (204), from the second wireless device (UE2), second information indicative of at least one beam measurement result for at least one of the Tx beams; and select (206), based on the second information, one of the plurality of Tx beams as an initial Tx beam to be used by the first wireless device (UE1) for the sidelink connection.

90. The first wireless device (UE1) of example 89, further configured to: perform the method according to any one of examples 1 to 88.

91. A method performed by a second wireless device (UE2) configured to communicate with a first wireless device (UE1) over a sidelink connection, the method comprising: performing (602) measurements of at least one of a plurality of transmission, Tx, beams of the first wireless device (UE1), the plurality of Tx beams transmitting first information; and transmitting (604), to the first wireless device (UE1), second information indicative of at least one beam measurement result obtained by performing the measurements of the at least one of the plurality of Tx beams.

92. The method of example 91, wherein the second information enables the first wireless device (UE1) to select, based on the second information, one of the plurality of Tx beams as an initial Tx beam to be used by the first wireless device (UE1) for the sidelink connection.

93. The method of example 92, wherein transmitting the second information triggers selection of the initial Tx beam by the first wireless device (UE1).

94. The method of any one of examples 91 to 93, wherein the second wireless device (UE2), after having transmitted the second information, performs at least one of the following steps: establishing the sidelink connection between the first wireless device (UE1) and the second wireless device (UE2); receiving data via the initial Tx beam from the first wireless device (UE2).

95. The method of any one of examples 91 to 94, wherein the second wireless device (UE2), before performing the measurements, performs at least one of the following steps: indicating, to the first wireless device (UE1), that the second wireless device (UE2) is configured to receive and/or transmit information over a sidelink connection; transmitting a request to the first wireless device (UE1) to select an initial Tx beam and/or establish a sidelink connection between the first wireless device (UE1) and the second wireless device (UE2); transmitting a link establishment acknowledgement to the first wireless device (UE1).

96. The method of example 95, wherein indicating, to the first wireless device (UE1), that the second wireless device (UE2) is configured to receive and/or transmit information over a sidelink connection comprises: transmitting, to the first wireless device (UE1), capability information.

97. The method of example 96, wherein the capability information indicates that the second wireless device (UE2) supports beamforming based sidelink transmission and/or reception.

98. The method of any one of examples 94 to 97, wherein performing the at least one step triggers the first wireless device (UE1) to transmit the first information over the plurality of Tx beams. 99. The method of any one of examples 91 to 98, wherein the second wireless device (UE2) receives the first information over one or more of the plurality of Tx beams.

100. The method of any one of examples 91 to 99, wherein the first information is beam-specific.

101. The method of any one of examples 91 to 100, wherein the first information received over Tx beams that are measured by the second wireless device (UE2) differs between at least two of the measured Tx beams.

102. The method of any one of examples 91 to 101, wherein the first information is indicative of the respective Tx beam and/or indicative of an index or identifier of the respective Tx beam.

103. The method of any one of examples 91 to 102, wherein the first information is indicative of an identity, ID, of the first wireless device (UE1).

104. The method of example 103, wherein the ID of the first wireless device (UE1) is included in the first information or derivable from the first information.

105. The method of example 103 or 104, wherein the ID of the first wireless device (UE1) is a layer two, L2, ID of the first wireless device (UE1) or a local ID associated with a layer two, L2, ID of the first wireless device (UE1).

106. The method of any one of examples 103 to 105, wherein the ID of the first wireless device (UE1) is derived by the second wireless device (UE2) from the first information using a mapping between the ID of the first wireless device (UE1) and at least a portion of the first information.

107. The method of any one of examples 103 to 106, wherein the ID of the first wireless device (UE1) is a local ID associated by a mapping to a layer two, L2, ID of the first wireless device (UE1).

108. The method of example 106 or 107, wherein the mapping is a mapping is between a layer two, L2, ID of the first wireless device (UE1) and a Sidelink Synchronization Signal Identity, SLSS ID.

109. The method of example 108, wherein the SLSS ID is assigned or selected during an initial L2 link establishment.

110. The method of any one of examples 106 to 109, wherein the mapping is preconfigured.

111. The method of any one of examples 106 to 110, further comprising: receiving the mapping or information indicative of the mapping from the first wireless device (UE1).

112. The method of example 111, wherein the mapping or the information indicative of the mapping is received in a discovery message or in a link establishment request message.

113. The method of any one of examples 103 to 112, wherein the ID of the first wireless device (UE1) is part of a Master Information Block, MIB.

114. The method of any one of examples 91 to 113, wherein at least one of the first information and the second information is carried by one or more of the following resources or signals:

Medium Access Control, MAC, Control Element, MAC CE;

Sidelink Control Information, SCI;

Sidelink Synchronization Signal Block, SL-SSB;

115. The method of any one of examples 91 to 114, wherein one or more resources for transmitting the second information are selected from a set of configured resources. 116. The method of example 115, wherein each configured resource spans one or more first elements in a frequency domain and one or more second elements in a time domain.

117. The method of example 116, wherein the one or more first elements comprise at least one of:

Physical Resource Blocks, PRBs; sub carriers; sub channels.

118. The method of example 116 or 117, wherein the one or more second elements comprise at least one of:

Orthogonal Frequency Division Multiplexing, OFDM, symbols; slots.

119. The method of any one of examples 115 to 118, wherein the configured resources are consecutively or non-consecutively distributed in at least one of frequency and time.

120. The method of any one of examples 115 to 119, wherein the configured resources are configured for the second wireless device (UE2) and at least one third wireless device (UE3).

121. The method of any one of examples 115 to 120, wherein the configured resources are configured for all wireless devices (UE1; UE2;

UE3) within a predefined spatial area.

122. The method of any one of examples 115 to 121, wherein the set or a subset of the configured resources is associated with at least one identity, ID, of a wireless device.

123. The method of any one of examples 115 to 122, wherein the set or a subset of the configured resources is associated with one or more layer two, L2, destination IDs.

124. The method of any one of examples 115 to 123, wherein the one or more resources are selected based on one or more of: an identity, ID, of the first wireless device (UE1); an identity, ID, of the second wireless device (UE2); an index of one or more of the Tx beams of the first wireless device (UE2); an indication of the one or more resources, the indication being received by the second wireless device (UE2).

125. The method of example 124, wherein the one or more of the Tx beams include a strongest Tx beam measured by the second wireless device (UE2).

126. The method of example 124 or 125, wherein the one or more of the Tx beams correspond to all Tx beams measured by the second wireless device (UE2) and having a measured signal strength above a predefined strength threshold.

127. The method of any one of examples example 124 to 126, further comprising: receiving the indication of the one or more resources from the first wireless device (UE1).

128. The method of any one of examples 115 to 127, wherein the selected one or more resources are associated with the measured Tx beams having a measured signal strength above a predefined strength threshold.

129. The method of any one of examples 115 to 128, wherein each of the configured resources has an associated resource index, and the one or more resources are selected based on the associated resource index or indices.

130. The method of example 129, wherein the associated index or indices are determined as result(s) of a formula using, as input parameter(s), at least one of the following: an identity, ID, of the first wireless device (UE1); an identity, ID, of the second wireless device (UE2); an index of one or more of the Tx beams of the second wireless device (UE2).

131. The method of example 130, wherein the one or more of the Tx beams include a strongest Tx beam measured by the second wireless device (UE2). 132. The method of example 130 or 131, wherein the one or more of the Tx beams correspond to all measured Tx beams having a measured signal strength above a predefined strength threshold.

132. The method of any one of examples 130 to 132, wherein the associated index of the one or more configured resources, CRI, to be selected is determined as a result of the following formula:

CRI = F (UE1_ID, UE2_ID, BI) mod (N), wherein F denotes a mathematical function, UE1_ID denotes the ID of the first wireless device (UE1), UE2_ID denotes the ID of the second wireless device (UE2) and BI denotes the index of the at least one Tx beam measured by the second wireless device (UE2), and N denotes a total number of the set of configured resources.

133. The method of any one of examples 115 to 132, wherein the one or more selected resources are associated with and/or indicated by a strongest Tx beam measured by the second wireless device (UE2).

134. The method of any one of examples 115 to 133, wherein the one or more selected resources are associated with and/or indicated by all measured Tx beams having a measured signal strength above a predefined strength threshold.

135. The method of any one of examples 115 to 134, wherein different ones or subsets of the configured resources are unique for different ones of the Tx beams.

135. The method of example 115, wherein the one or more resources are randomly selected from the set of configured resources.

136. The method of any one of examples 115 to 135, wherein the one or more resources are selected by the second wireless device (UE2).

137. The method of any one of examples 115 to 135, wherein the set of configured resources is configured by a base station. 138. The method of example 137, further comprising: receiving, from the base station, an indication of the set of configured resources.

139. The method of example 138, wherein the set of configured resources is indicated by at least one of the following: system information; master information;

Radio Resource Control, RRC, signaling;

MAC CE; layer one, LI, signaling.

140. The method of any one of examples 91 to 139, further comprising: selecting, by the second wireless device (UE2), one or more Tx beams of the second wireless device (UE2); and transmitting the second information over the selected one or more Tx beams of the second wireless device (UE2).

141. The method of example 140, wherein the one or more Tx beams of the second wireless device (UE2) are selected based on a measurement report of the first wireless device (UE1) indicative of measurement results of measurements of the Tx beams of the second wireless device (UE2).

142. The method of example 140 or 141, wherein the second wireless device (UE2) performs beam sweeping to select the one or more of the Tx beams of the second wireless device (UE2).

142. The method of any one of examples 140 to 142, wherein the second wireless device (UE2) selects the one or more Tx beams based on corresponding reception, Rx, beams of the second wireless device (UE2) used to receive the first information from the first wireless device (UE1).

143. The method of any one of examples 140 to 142, wherein the second wireless device (UE2) is configured to select the one or more Tx beams based on beam correspondence.

144. The method of any one of examples 91 to 143, wherein the measurements are performed in a first time slot and the second information is transmitted in a second time slot different from the first time slot.

145. The method of example 144, wherein the first time slot and the second time slot fulfil at least one of the following criteria: they are timely disjunct; they are separated in time; the are non-overlapping.

146. The method of any one of examples 91 to 145, wherein the second information is transmitted when the transmission of the first information over the plurality of Tx beams of the first wireless device (UE1) is finished.

147. The method of any one of examples 91 to 146, wherein the second information is transmitted after each time the transmission of the first information over the plurality of Tx beams of the first wireless device (UE1) is finished.

148. The method of any one of examples 91 to 147, wherein the second information is transmitted when a beam sweep by the first wireless device (UE1) using the plurality of Tx beams of the first wireless device (UE1) is finished.

149. The method of any one of examples 91 to 148, wherein the second information is transmitted after each time a beam sweep by the first wireless device (UE1) using the plurality of Tx beams of the first wireless device (UE1) is finished.

150. The method of any one of examples 91 to 149, wherein the second information is transmitted after each measurement of a beam strength of the Tx beams of the first wireless device (UE1) that is performed by the second wireless device (UE2).

151. The method of any one of examples 91 to 150, wherein the second information is transmitted when a beam strength of a Tx beam of the first wireless device (UE1) that is measured by the second wireless device (UE2) is above a predefined strength threshold. 152. The method of any one of examples 91 to 151, further comprising: transmitting location information to at least one of: the first wireless device (UE1); a third wireless device (UE3); a base station.

153. The method of example 152, wherein the location information is indicative of at least one of the following: a previous location of the second wireless device (UE2); a current or previous movement velocity of the second wireless device (UE2); a current or previous movement path of the second wireless device (UE2); information indicative of a regular behavior of the second wireless device (UE2).

154. The method of example 152 or 153, wherein the location information is indicative of or based on a prediction of the location of the second wireless device (UE2).

155. The method of example 154, wherein the prediction of the location of the second wireless device (UE2) is based on at least one of the following: a previous location of the second wireless device (UE2); a current or previous movement velocity of the second wireless device (UE2); a current or previous movement path of the second wireless device (UE2); information indicative of a regular behavior of the second wireless device (UE2).

156. The method of example 154 or 155, wherein the prediction is determined by an artificial intelligence module and/or a trained machine learning model.

157. The method of any one of examples 152 to 156, wherein the location information comprises at least one of the following: a position of the second wireless device (UE2) determined using a global navigation satellite system, GNSS; an identity, ID, of a cell serving the second wireless device (UE2); an identity, ID, of a base station serving the second wireless device (UE2); one or more position measurement results.

158. The method of example 157, wherein the one or more position measurement results comprise at least one of the following: a Time Difference of Arrical, TDOA; a Round Trip Time, RTT; a Multi-Round Trip Time, Multi-RTT; an Angle of departure, AoD; an Angle of Arrival, AoA.

159. The method of any one of examples 91 to 156, wherein the plurality of Tx beams consists of multiple subsets of Tx beams and the second wireless device (UE2) receives the first information over one subset of Tx beams at a time.

160. The method of any one of examples 91 to 159, wherein the second wireless device (UE2) receives the first information over different Tx beams of the plurality of Tx beams at different time instants.

161. The method of any one of examples 91 to 160, wherein the second wireless device (UE1) receives the first information over the plurality of Tx beams by receiving the first information over one Tx beam at a time.

162. The method of any one of examples 91 to 161, wherein the first information is received within a time window.

163. The method of example 162, further comprising: receiving, from the first wireless device (UE1), an indication of at least one temporal location associated with the time window.

164. The method of example 163, wherein the at least one temporal location comprises one or more of: a start time of the time window; a halftime of the time window; an end time of the time window.

165. The method of example 163 or 164, wherein receiving the indication of the at least one temporal location associated with the time window comprises receiving, from the first wireless device (UE1), a first SL- SSB or CSI-RS in a SL-SSB or CSI-RS resource associated with the at least one temporal location.

166. The method of example 163 or 164, wherein receiving the indication of the at least one temporal location associated with the time window comprises receiving, from the first wireless device (UE1), a first SL- SSB or CSI-RS using a SL-SSB or CSI-RS sequence associated with the at least one temporal location.

167. The method of example 163 or 164, wherein receiving the indication of the at least one temporal location associated with the time window comprises receiving, from the first wireless device (UE1), a message including a bit or flag indicative of the at least one temporal location.

168. The method of example 167, wherein the message comprises one or more of:

Sidelink Control Information, SCI;

Medium Access Control, MAC, Control Element, MAC CE;

Medium Access Control Protocol Data Unit, MAC PDU, header.

169. The method of any one of examples 162 to 168, wherein a length of the time window and/or a number of emissions in the time window is preconfigured.

170. The method of any one of examples 162 to 169, wherein the time window, including the reception of the first information, is repeated at least twice.

171. The method of example 170, wherein the time window, including the reception of the first information, is repeated periodically.

172. The method of any one of examples 91 to 171, wherein resources used for transmitting the first information and/or the second information differ from other resources that fulfil at least one of the following criteria: the other resources are used in a sidelink connection of the first wireless device (UE1); the other resources are used in a sidelink connection of the second wireless device (UE2); the other resources are used in a selection of a non-initial beam.

173. The method of example 172, wherein the resources used for transmitting the first information and/or the second information differ from the other resources in at least one of a time domain and a spatial domain.

174. The method of example 172 or 173, wherein transmission time points used for transmitting the first information and/or the second information differ, by a time offset, from transmission time points used for transmitting and/or receiving information via the sidelink connection.

175. The method of example 174, further comprising: receiving, from the first wireless device (UE2), a mapping between the time offset and an identity, ID, of the first wireless device (UE1).

176. The method of example 175, wherein the mapping is included in at least one of: a discovery message received by the second wireless device (UE2) from the first wireless device (UE1); a sidelink establishment request message received by the second wireless device (UE2) from the first wireless device (UE1).

177. The method of any one of examples 91 to 176, wherein resources used for transmitting the first information and/or the second information are specific for the pair of the first wireless device (UE1) and the second wireless device (UE2).

178. The method of any one of examples 91 to 177, further comprising: receiving, from the first wireless device (UE1), an indication that an initial Tx beam is to be selected by the first wireless device (UE1) and/or that the second wireless device (UE2) shall perform the measurements. 179. The method of example 178, wherein receiving the indication comprises receiving, from the first wireless device (UE2), at least one of the following: a Medium Access Control, MAC, Control Element, MAC CE; a MAC CE without any accompanying data; a link establishment request; a direct communication request; a PC5 signaling; a PC5-Radio Resource Control, -RRC, signaling; a layer one, LI, signaling.

180. The method of example 179, wherein the LI signaling is carried on a physical channel other than Physical Sidelink Shared Channel, PSSCH, Physical Sidelink Control Channel, PSCCH, and Physical Sidelink Feedback Channel, PSFCH.

181. The method of any one of examples 91 to 180, further comprising: transmitting, to the first wireless device (UE1), an indication of resources used for transmitting the second information from the second wireless device (UE2) to the first wireless device (UE1).

182. The method of any one of examples 91 to 181, wherein the second information and the first information are carried on resources that are similar in at least one of a frequency and a code domain.

183. The method of example 182, wherein the resources are exclusively used by the first wireless device (UE1) to transmit the first information during a first time period and exclusively used by the second wireless device (UE2) to transmit the second information during a second time period differing from the first time period.

184. The method of example 183, wherein the first time period and the second time period are timely disjunct.

185. The method of example 183 or 184, further comprising: indicating at least one of the first time period and the second time period to the first wireless device (UE1).

185. The method of any one of examples 183 to 184, wherein the second time period starts upon or after at least one of the following conditions being fulfilled: the second wireless device (UE2) has transmitted the second information; the second wireless device (UE2) has transmitted, to the first wireless device (UE1), a Channel State Information, CSI, report; the first wireless device (UE1) has selected the initial Tx beam.

186. The method of any one of examples 91 to 185, wherein the second information is indicative of at least one of the following: a strongest measured Tx beam; a signal strength of the strongest measured Tx beam; signal strengths of all measured Tx beams that are above a predefined signal strength threshold; signal strengths of all measured Tx beams; one or more parameters for at least one of the measured Tx beams; an identity, ID, of the second wireless device (UE2).

187. The method of example 186, wherein the one or more parameters include: Rank Indicator, RI;

Channel Quality Indicator, CQI;

Reference Signal, RS, Resource Indicator;

Reference Signal Received Power, RSRP; and/or Signal to Noise Ratio, SINR.

188. The method of example 186 or 187, wherein the at least one of the measured Tx beams corresponds to the strongest measured Tx beam.

189. A second wireless device (UE2) configured to communicate with a first wireless device (UE1) over a sidelink connection, the second wireless device (UE2) further configured to: perform (602) measurements of at least one of a plurality of transmission, Tx, beams of the first wireless device (UE1), the plurality of Tx beams transmitting first information; and transmit (604), to the first wireless device (UE1), second information indicative of at least one beam measurement result obtained by performing the measurements of the at least one of the plurality of Tx beams. 190. The second wireless device (UE2) of example 189, further configured to perform the method according to any one of examples 91 to 188.

191. A communication system (100) comprising: the first wireless device (UE1) according to example 89 or 90; and the second wireless device (UE2) according to example 189 or 190.

192. The communication system of example 191, further comprising: a base station configured to communicate with at least one of the first wireless device (UE1) and the second wireless device (UE2).

193. A storage medium storing instructions which, when executed by at least one processor of a first wireless device (UE1) configured to communicate with a second wireless device (UE2) over a sidelink connection, cause the first wireless device (UE1) to perform the method according to any one of examples 1 to 88.

194. A storage medium storing instructions which, when executed by at least one processor of a second wireless device (UE2) configured to communicate with a first wireless device (UE1) over a sidelink connection, cause the second wireless device (UE2) to perform the method according to any one of examples 91 to 188.

Further modifications and advantages of the technique disclose herein may become apparent to those skilled in the art.

Claims

1. A method performed by a second wireless device (UE2) configured to communicate with a first wireless device (UE1) over a sidelink connection, the method comprising: performing (602) measurements of at least one of a plurality of transmission, Tx, beams of the first wireless device (UE1), the plurality of Tx beams transmitting first information; and transmitting (604), to the first wireless device (UE1), second information indicative of at least one beam measurement result obtained by performing the measurements of the at least one of the plurality of Tx beams.

2. The method of claim 1, wherein one or more resources for transmitting the second information are selected from a set of configured resources.

3. The method of claim 1 or 2, wherein the set or a subset of the configured resources is associated with at least one identity, ID, of a wireless device.

4. The method of claim 2 or 3, wherein the set or a subset of the configured resources is associated with one or more layer two, L2, destination IDs.

5. The method of any one of claims 2 to 4, wherein the one or more resources are selected based on one or more of: an identity, ID, of the first wireless device (UE1); an identity, ID, of the second wireless device (UE2); an index of one or more of the Tx beams of the first wireless device (UE2); an indication of the one or more resources, the indication being received by the second wireless device (UE2).

6. The method of any one of claims 2 to 5, wherein each of the configured resources has an associated resource index, and the one or more resources are selected based on the associated resource index or indices.

7. The method of claim 6, wherein the associated index or indices are determined as result(s) of a formula using, as input parameter(s), at least one of the following: an identity, ID, of the first wireless device (UE1); an identity, ID, of the second wireless device (UE2); an index of one or more of the Tx beams of the second wireless device (UE2).

8. The method of claim 7, wherein the associated index of the one or more configured resources, CRI, to be selected is determined as a result of the following formula:

9. The method of any one of claims 1 to 8, wherein the one or more resources are selected by the second wireless device (UE2).

10. The method of any one of claims 1 to 9, further comprising: transmitting, to the first wireless device (UE1), an indication of resources used for transmitting the second information from the second wireless device (UE2) to the first wireless device (UE1).

11. A second wireless device (UE2) configured to communicate with a first wireless device (UE1) over a sidelink connection, the second wireless device (UE2) being configured to perform the method according to any one of claims 1 to 10.

12. A method performed by a first wireless device (UE1) configured to communicate with a second wireless device (UE2) over a sidelink connection, the method comprising: transmitting (202) first information over a plurality of transmission, Tx, beams; receiving (204), from the second wireless device (UE2), second information indicative of at least one beam measurement result for at least one of the Tx beams; and selecting (206), based on the second information, one of the plurality of Tx beams as an initial Tx beam to be used by the first wireless device (UE1) for the sidelink connection.

13. The method of claim 12, further comprising: receiving, from the second wireless device (UE2), an indication of resources used for transmitting the second information from the second wireless device (UE2) to the first wireless device (UE1).

14. The method of claim 12 or 13, wherein one or more resources for transmitting the first information are selected from a set of configured resources, wherein, optionally,

{a} the one or more resources are selected based on an identity, ID, of the first wireless device (UE1) and/or an identity, ID, of the second wireless device (UE2); and/or

{b} each of the configured resources has an associated resource index, and the one or more resources are selected based on the associated resource index or indices.

15. A first wireless device (UE1) configured to communicate with a second wireless device (UE2) over a sidelink connection, the first wireless device being further configured to perform the method according to any one of claims 12 to 14.

16. A storage medium storing instructions which, when executed by at least one processor of a first wireless device (UE1) configured to communicate with a second wireless device (UE2) over a sidelink connection, cause the first wireless device (UE1) to perform the method according to any one of claims 12 to 14 or which, when executed by at least one processor of a second wireless device (UE2) configured to communicate with a first wireless device (UE1) over a sidelink connection, cause the second wireless device (UE2) to perform the method according to any one of claims

1 to 10.