CONTROL TECHNICAL FIELD

The present disclosure relates generally to the field of wireless communication, particularly of feedback messages for groupcast power control. To this end, the disclosure proposes a Target User Equipment (UE) that selects a feedback resource and sends a power control feedback message to a Source UE. The disclosure also proposes a Source UE that sends a transmission to a Target UE and receives the power control feedback message.

BACKGROUND

Generally, a groupcast transmission is the transmission from a Transmit User Equipment (Tx UE) to a group of Receive UEs (Rx UEs) in the sidelink as it is depicted in FIG. 12. In the diagram 1200, illustrating conventional groupcast transmission, the Tx UE 1201 sends a groupcast transmission to Rx UE A 1202, Rx UE B 1203, Rx UE C 1204, Rx UE D 1205 and Rx UE E 1206. Power control for groupcast can enable efficient power usage and interference reduction. For groupcast power control, the Tx UE may determine the transmit power for the groupcast transmission based on, for example, the sidelink path-losses between the Tx UE and the Rx UEs. Furthermore, the Tx UE may obtain the path-losses from the Tx UE to the Rx UEs based on feedback from the Rx UEs, e.g., via a dedicated feedback resource for each Rx UE, which may lead to an increasing feedback overhead with increasing number of Rx UEs. In addition, as the number of Rx UEs in a groupcast transmission can be varying, this also leads to a varying feedback overhead.

Moreover, for New Radio (NR) Vehicle-to-Everything (V2X), it is supported that for unicast, groupcast and broadcast the sidelink power control is based on the path-loss between the Tx UE and the Next generation NodeB (gNB) (i.e., if the Tx UE is in coverage of the network). A unicast transmission is the transmission from a Tx UE to Rx UE in the sidelink. Also, it is supported in NR V2X that at least for unicast, the sidelink power control can be based on the path-loss between the Tx UE and Rx UE. Conventionally, in the case of unicast, the sidelink path-loss for power control can be derived at the Tx UE based on feedback of the Sidelink Reference Signal Received Power (SL-RSRP) from the Rx UE. For example, the Tx UE sends a reference signal with a given transmit power, which enables the Rx UE to estimate the SL- RSRP. Afterwards, the Rx UE feeds back the estimated SL-RSRP to the Tx UE. Furthermore, based on the fed back SL-RSRP and the transmit power used to send the reference signal, the Tx UE can derive the path-loss from the Tx UE to the Rx UE. The sidelink power control for groupcast can also be based on the path-losses from the Tx UE to the Rx UEs for an efficient power usage. For instance, similar to the unicast, the Tx UE can derive the path-losses to the Rx UEs based on fed back SL-RSRP from the Rx UEs, and by assuming a dedicated feedback resource for each Rx UE for the SL-RSRP report from each Rx UE. This leads, however, to an increasing overhead with increasing group size. Besides, the (varying) number of Rx UEs in the group needs to be known for allocating resources and, moreover, the Rx UEs need to be configured to send feedback on a given dedicated resource.

A possible method for reducing the feedback overhead may include having only the Rx UE with the worst SL-RSRP to feed back its SL-RSRP. Nevertheless, prior information about the Rx UEs is required at the Tx UE, when prior unicast connections from the Tx UE to the Rx UEs is assumed, or feedback from the Rx UEs may be needed to enable the Tx UE to determine which Rx UE should feedback its SL-RSRP. Moreover, with only the worst SL-RSRP the power control may only be based on the largest sidelink path-loss, whereas the power control could be a function of the path-losses to several Rx UEs. Also, group-based feedback may be used to feedback the worst SL-RSRP to the Tx UE, i.e., the Rx UEs report their SL-RSRP to a lead UE, which could then determine the worst SL-RSRP and feed it back to the TX UE. Furthermore, with group-based feedback, resources for the feedback of the Rx UEs is shifted from the uplink to sidelink, and in addition, a lead UE needs to be selected and configured among the Rx UEs.

For the SL-RSRP report for groupcast power control, ranges of SL-RSRPs have also been proposed. For instance, based on the measured SL-RSRP, an Rx UE is aware of the SL-RSRP range it belongs to. Also, the Rx UEs belonging to the same SL-RSRP range (may) share a common resource for SL-RSRP feedback. Moreover, based on the feedback, the Tx UE is aware of the SL-RSRP distribution of Rx UEs and in turn, of the distribution of the path-loss to the Rx UEs, which may be used for the groupcast power control. Although the proposed approach enables reduction of the feedback overhead for groupcast power control, grouping UEs based on RSRP ranges has some limitations. The SL-RSRP ranges, i.e., the thresholds of the SL- RSRP ranges, depend on the Tx power used by the Tx UE to send the reference signal, which may differ among different Tx UEs and the corresponding groups. For example, to mitigate interference at the gNB, a Tx UE near the gNB may transmit with lower power than a Tx UE farther away from the gNB, i.e., due to the distinct path-losses from the two Tx UEs to the gNB. As the SL-RSRP ranges depend on the Tx power of the Tx UE, i.e., they are determined by the Tx UE, this may lead to different sets of SL-RSRP ranges configured per Tx UE or group. Furthermore, the RSRP measurements may also fluctuate as they highly depend on the channel conditions.

SUMMARY In view of the above-mentioned problems and disadvantages, embodiments of the present invention aims to improve the conventional devices and methods for supporting power control based on UE feedback mechanism An objective is in particular to provide a Target UE (Rx UE) and a Source UE (Tx UE), and corresponding methods for supporting such a UE feedback mechanism (e.g., a groupcast feedback mechanism). Feedback for power control based on distance (Tx-Rx distance) between the Target UE and the Source UE is specifically discussed.

The objective is achieved by the embodiments provided in the enclosed independent claims. Advantageous implementations of the embodiments of the present invention are further defined in the dependent claims.

A first aspect of the invention provides a Target User Equipment (UE) for performing power control feedback, the Target UE configured to obtain its distance to a Source UE, select a feedback resource depending on whether the obtained distance is below, above or equal to one or more distance thresholds, and send a power control feedback message to the Source UE on the selected feedback resource.

The Target UE may be, for example, a receive (Rx) UE of a groupcast transmission. Moreover, the Source UE may be, for example, the Tx UE of a groupcast transmission. Hereinafter, the terms ‘'Target UE” and “Rx UE” are used interchangeably, without limiting the present disclosure. Moreover, the terms “Source UE” and “Tx UE” are also used interchangeably. The Target UE is also a transmit device, e.g. when it sends a feedback message. The Source UE is also a receive device, e.g. when it receives a feedback message. The Target UE obtains its distance to the Source UE. For example, in some embodiments, the Target UE may obtain its distance to the Source UE by estimating the distance by itself. In some embodiments, the distance may be determined in another way, e.g., it may be provided by the Source UE.

Moreover, the one or more distance thresholds may be (pre)configured or provided by, e.g., the Source UE, the network, etc. Moreover, the Target UE may obtain the one or more distance thresholds and may have these values. The Target UE of the first aspect supports a UE feedback mechanism for groupcast power control (e.g., a groupcast feedback mechanism), specifically according to the distance thresholds, i.e., based on a distance between the Target UE and the Source UE.

The Target UE may comprise a circuitry. The circuitry may comprise hardware and software. The hardware may comprise analog or digital circuitry, or both analog and digital circuitry. In some embodiments, the circuitry comprises one or more processors and a non-volatile memory connected to the one or more processors. The non-volatile memory may carry executable program code which, when executed by the one or more processors, causes the device to perform the operations or methods described herein.

In an implementation form of the first aspect, the feedback resource is selected based on whether the obtained distance is within a distance range, and wherein the distance range is defined by a first distance threshold and a second distance threshold.

Hereinafter, the terms “distance range” and ‘Tx-Rx distance range” are used interchangeably, without limiting the present disclosure.

In a further implementation form of the first aspect, the power control feedback message is sent based on a Sidelink Reference Signal Received Power (SL-RSRP) of the Target UE.

In particular, the Target UE may measure the SL-RSRP of a reference signal sent by the Source

UE. In some embodiments, the Target UE may be configured to send a feedback message on a shared feedback resource based on its distance to a Source UE (Tx-Rx distance), i.e., based on a Tx-Rx distance threshold or a Tx-Rx distance range. In addition, in some embodiments, the Target UE may send the feedback considering also whether the measured SL-RSRP of the Target UE is above a (pre)configured SL-RSRP threshold. The SL-RSRP threshold can be dependent on the Quality of Service (QoS) requirements. Furthermore, each Tx-Rx distance range may have a different SL-RSRP threshold, where the SL-RSRP threshold could be dependent on the Tx-Rx distance thresholds defining a Tx-Rx distance range. For the feedback message, the Target UE may send an indicator whether its measured SL-RSRP is above the SL- RSRP threshold or optionally, when the SL-RSRP is less than or equal to the SL-RSRP threshold. The Tx-Rx distance ranges may be dependent on the communication range requirement. For the feedback, another metric instead of SL-RSRP, e.g., Receive Signal Received Quality (RSRQ), could also be considered. In a further implementation form of the first aspect, the power control feedback message comprises an indicator of the SL-RSRP.

Moreover, in the case of one SL-RSRP threshold, for example: in some embodiments, the Target UE may be configured to feed back an indicator, if the SL-RSRP is above the SL-RSRP threshold. In some embodiments, the Target UE may be configured to feed back an indicator, if the SL-RSRP is below or equal to the SL-RSRP threshold. In some embodiments, the Target UE may be configured to feed back an indicator #1 if the SL-RSRP is below the SL-RSRP threshold, and feedback an indicator #2 if the SL-RSRP is below or equal to the SL-RSRP threshold, where the indicator #1 and the indicator #2 are to be distinguished at the Source UE. In some embodiments, the Target UE may be configured to feed back an indicator on a first feedback resource if the SL-RSRP is above the SL-RSRP threshold, or feedback an indicator on a second feedback resource if the SL-RSRP is below or equal to the SL-RSRP threshold.

Moreover, the Target UE may be configured to feed back the SL-RSRP.

In a further implementation form of the first aspect, the indicator is obtained based on a comparison of the SL-RSRP with one or more SL-RSRP thresholds. In particular, the one or more SL-RSRP thresholds may be (pre)configured or provided by the Source UE or network.

In a further implementation form of the first aspect, the feedback resource is further selected based on a comparison of the SL-RSRP with the one or more SL-RSRP thresholds, and wherein the indicator is defined by the feedback resource.

In particular, the feedback resource may also be selected depending on whether the SL-RSRP is below, equal or above the one or more SL-RSRP thresholds.

In a further implementation form of the first aspect, the feedback resource is selected based on whether the SL-RSRP is within a SL-RSRP range, and wherein the SL-RSRP range is defined by a first SL-RSRP threshold and a second SL-RSRP threshold. In a further implementation form of the first aspect, each distance range is associated with one or more specific SL-RSRP thresholds.

In a further implementation form of the first aspect, the Target UE is further configured to obtain one or more distance sub-ranges located within each distance range, determine, whether the obtained distance is within one of the distance sub-ranges, select, when it is determined that the obtained distance is within a distance sub-range, a feedback resource associated with that determined distance sub-range, and send a successive power control feedback message to the Source UE on the selected feedback resource. In particular, the one or more distance sub-ranges may be (pre)configured or provided by the Source UE or network. The successive power control feedback message may provide additional information to the Source UE for the groupcast power control.

In a further implementation form of the first aspect, the successive power control feedback message comprises an indicator obtained based on a comparison of the SL-RSRP with one or more SL-RSRP thresholds.

In particular, the one or more SL-RSRP thresholds may be (pre)configured or provided by the Source UE or network. A second aspect of the invention provides a method for a Target User Equipment (UE), the method comprises obtaining, a distance between the Target UE and a Source UE, selecting a feedback resource depending on whether the obtained distance is below, above or equal to one or more distance thresholds, and sending a power control feedback message to the Source UE on the selected feedback resource.

In some embodiments, the one or more distance thresholds may be (pre)configured or provided by the Source UE or network.

In an implementation form of the second aspect, the feedback resource is selected based on whether the obtained distance is within a distance range, and wherein the distance range is defined by a first distance threshold and a second distance threshold.

In a further implementation form of the second aspect, the power control feedback message is sent based on a SL-RSRP of the Target UE.

In a further implementation form of the second aspect, the power control feedback message comprises an indicator of the SL-RSRP.

In a further implementation form of the second aspect, the indicator is obtained based on a comparison of the SL-RSRP with one or more SL-RSRP thresholds.

In a further implementation form of the second aspect, the feedback resource is further selected based on a comparison of the SL-RSRP with the one or more SL-RSRP thresholds, and wherein the indicator is defined by the feedback resource.

In a further implementation form of the second aspect, the feedback resource is selected based on whether the SL-RSRP is within a SL-RSRP range, and wherein the SL-RSRP range is defined by a first SL-RSRP threshold and a second SL-RSRP threshold.

In a further implementation form of the second aspect, each distance range is associated with one or more specific SL-RSRP thresholds. In a further implementation form of the second aspect, the method further comprises obtaining one or more distance sub-ranges located within each distance range, determining, whether the obtained distance is within one of the distance sub-ranges, selecting, when it is determined that the obtained distance is within a distance sub-range, a feedback resource associated with that determined distance sub-range, and sending a successive power control feedback message to the Source UE on the selected feedback resource.

In a further implementation form of the second aspect, the successive power control feedback message comprises an indicator obtained based on a comparison of the SL-RSRP with one or more SL-RSRP thresholds.

A third aspect of the invention provides a Source User Equipment (UE) for performing power control of a transmission, the Source UE configured to send a transmission to two or more Target UEs, and receive, from at least one Target UE, a respective power control feedback message on at least one feedback resource depending on whether an obtained distance from the

Source UE to the at least one Target UE is below, above or equal to one or more distance thresholds.

The Source UE may be, for example, the Tx UE.

In particular, the Source UE may be configured to send a reference signal to two or more Target UEs.

In some embodiments, not receiving any feedback also provides information to the Source UE, e.g., the Source UE may know that the Target UE(s) are not within the distance ranges or do not have a minimum SL-RSRP.

The Source UE may comprise a circuitry. The circuitry may comprise hardware and software. The hardware may comprise analog or digital circuitry, or both analog and digital circuitry. In some embodiments, the circuitry comprises one or more processors and a non-volatile memory connected to the one or more processors. The non-volatile memory may carry executable program code which, when executed by the one or more processors, causes the device to perform the operations or methods described herein. In an implementation form of the third aspect, the Source UE is further configured to: estimate, based on the received power control feedback message, at least one path-loss from the Source UE to at least one Target UE, or at least one Sidelink Reference Signal Received Power, SL- RSRP of at least one Target UE, and determine a sidelink power level based on the estimated at least one path-loss or the estimated at least one SL-RSRP.

A fourth aspect of the invention provides a method for a Source UE, the method comprises sending a transmission to two or more Target UEs, and receiving, from at least one Target UE, a respective power control feedback message on at least one feedback resource depending on whether an obtained distance from the Source UE to the at least one Target UE is below, above or equal to one or more distance thresholds.

The one or more distance thresholds may be (pre)configured or provided by the network. In an implementation form of the fourth aspect, the method further comprises estimating, based on the received power control feedback message, at least one path-loss from the Source UE to at least one Target UE, or at least one Sidelink Reference Signal Received Power, SL-RSRP of at least one Target UE, and determining a sidelink power level based on the estimated at least one path-loss or the estimated at least one SL-RSRP.

A fifth aspect of the invention provides a computer program which, when executed by a computer, causes the method of the second aspect or one of the implementation form of the second aspect and/or the fourth aspect or one of the implementation form of the fourth aspect to be performed.

In some embodiments, the computer program can be provided on a non-transitory computer- readable recording medium.

It has to be noted that all devices, elements, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

The above described aspects and implementation forms of the present invention will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which

FIG. 1 is a schematic view of a Target UE for performing power control feedback, according to an embodiment of the present invention.

FIG. 2 is a schematic view of a Source UE for performing power control of a transmission, according to an embodiment of the present invention.

FIG. 3 is a schematic view of distance ranges and selecting the feedback resource.

FIG. 4 is a schematic view of selecting the feedback resource based on distance ranges and a SL-RSRP threshold.

FIG. 5 is a schematic view of a flowchart of a method for sending the power control feedback message based on distance ranges.

FIG. 6 is a schematic view of a flowchart of a method for sending the power control feedback message based on the distance ranges and a SL-RSRP threshold. FIG. 7 is a schematic view of a flowchart of a method including one SL-RSRP threshold per each distance range.

FIG. 8 is a schematic view of selecting the feedback resource when having one distance range and with a SL-RSRP threshold. FIGs. 9a and 9b are schematic views of sending a successive power control feedback message.

FIG. 10 is a flowchart of a method for a Target UE, according to an embodiment of the invention.

FIG. 11 is a flowchart of a method for a Source UE, according to an embodiment of the invention. FIG. 12 schematically illustrates a conventional groupcast transmission.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic view of a Target UE 100 for performing power control feedback, according to an embodiment of the present invention.

The Target UE 100 configured to obtain its distance 101 to a Source UE 110.

The Target UE 100 is further configured to select a feedback resource 102 depending on whether the obtained distance 101 is below, above or equal to one or more distance thresholds 103.

The Target UE 100 is further configured to send a power control feedback message 104 to the Source UE 110 on the selected feedback resource 102. The Target UE may comprise a circuitry. The circuitry may comprise hardware and software. The hardware may comprise analog or digital circuitry, or both analog and digital circuitry. In some embodiments, the circuitry comprises one or more processors and a non-volatile memory connected to the one or more processors. The non-volatile memory may carry executable program code which, when executed by the one or more processors, causes the device to perform the operations or methods described herein.

FIG. 2 is a schematic view of a Source UE 110 for performing power control of a transmission, according to an embodiment of the present invention. The Source UE 110 configured to send a transmission 201 to two or more Target UEs 100.

The Source UE 110 is further configured to receive, from at least one Target UE 100, a respective power control feedback message 104 on at least one feedback resource 102 depending on whether an obtained distance 101 from the Source UE 110 to the at least one Target UE 100 is below, above or equal to one or more distance thresholds 103.

The Source UE may comprise a circuitry. The circuitry may comprise hardware and software. The hardware may comprise analog or digital circuitry, or both analog and digital circuitry. In some embodiments, the circuitry comprises one or more processors and a non-volatile memory connected to the one or more processors. The non-volatile memory may carry executable program code which, when executed by the one or more processors, causes the device to perform the operations or methods described herein.

Reference is made to FIG. 3, which is a schematic view of distance ranges 301, 302, 303 and selecting the feedback resource 102, for example, based on the distance ranges 301, 302 and

303.

The Target UE 100 (Rx UE) may select the feedback resource 102 from the available feedback resources 102, 304, 306 based on the distance ranges 301, 302, 303.

For groupcast power control, the feedback message 104 from the Target UE 100 (Rx UE) may be sent based on (pre)configured distance ranges 301, 302, 303 (i.e., ranges of Tx-Rx distance) as well as based on a SL-RSRP threshold 305 for each distance range 301, 302, 303.

For example, each distance range 301, 302, 303 (Tx-Rx distance range) may be defined by a lower distance threshold (the first distance threshold) and an upper distance threshold (the second distance threshold). The Tx-Rx distance ranges 301, 302, 303 may or may not be continuous or adjacent to one another. Without loss of generality, in the following, it is assumed that the Tx-Rx distance ranges 301, 302, 303 are continuous and adjacent to one another.

For example, by assuming having N number of distance ranges, the Tx-Rx distance ranges 301, 302, 303 are defined by (pre)configured Tx-Rx distance thresholds D ₀ , D _{1 ,} ... D _N where D ₀ < D ₁ < ... < D _N with a determined Tx-Rx distance range t 302 is defined by the lower (the first) and upper (the second) thresholds and D _i , respectively.

For the power control feedback message 104 of the Target UE 100 (Rx UEs), a shared feedback resource 102, 304, 306 is associated with each Tx-Rx distance range 301, 302, 303 as depicted in FIG. 3. For example, the feedback resource 102 is associated with the distance range t indicated by reference 302. Moreover, the (pre)configured SL-RSRP threshold 305 for distance range t 302 is denoted by R _i 305. A feedback scheme is proposed based on the SL-RSRP measured by the Target UE 100 (Rx UE) along with the Tx-Rx distance of the Rx UE 100, i.e., the distance 101 between the Tx UE 110 and the Rx UE 100. The Target UE 100 (Rx UE) can determine its Tx-Rx distance 101 based on its own location and the Source UE’s 110 (Tx UE’s) location, which can be indicated by the Source UE, e.g., in the Sidelink Control Information (SCI). The Tx-Rx distance 101 can also be obtained without the knowledge of the Source UE’s location, e.g., via relative (distance) positioning at the Target UE 100. The Tx-Rx distance 101 can also be determined in other ways.

Moreover, if the Tx-Rx distance 101 of the Target UE 100 (Rx UE) lies within Tx-Rx distance range t 302, i.e., it satisfies “D _i-1 < Tx-Rx distance 101 < D ”, and the SL-RSRP of the Rx UE satisfies: SL-RSRP > R _i 305, the Target UE 100 (Rx UE) sends indicator #1 (which carries one bit of information) on the feedback resource 102 associated with the Tx-Rx distance range t 302.

Moreover, if the Tx-Rx distance 101 of the Target UE 100 (Rx UE) lies within Tx-Rx distance range t 302, i.e., it satisfies “D _i-1 < Tx-Rx distance 101 <D _i ”, and the SL-RSRP of Target UE 100 (Rx UE) satisfies “SL-RSRP < R ₁ 305”, the Target UE 100 (Rx UE) sends indicator #2 (which carries one bit of information) on the feedback resource 102 associated with the Tx- Rx distance range t 302.

Indicator #1 and indicator #2 need to be distinguished at the Source UE 110 (Tx UE), i.e., they could be two orthogonal sequences, enabling the Source UE 110 (Tx UE) to determine whether the feedback corresponds to a SL-RSRP report which is less than or equal or above the SL- RSRP threshold for a given Tx-Rx distance range 301, 302, 303. Reference is made to FIG. 4, which is a schematic view of selecting the feedback resource 401, 402 based on distance ranges 301, 302, 303 and the SL-RSRP threshold 305.

As a feedback resource 102, 304, 306 is actually defined by a time, frequency, and code resource, the two types of indicators described above could also be provided over two different time-frequency resources per range, i.e., there would be 2N feedback time-frequency resources for N Tx-Rx distance ranges, for example, two feedback resources associated with each Tx-Rx distance range (one for indicator #1 and one for indicator #2) as it is shown in FIG. 4. For instance, two feedback resources 401 and 402 are associated with the distance range 302 (the feedback resource 401 is for indicator #1 and the feedback resource 402 is for indicator #2) as it is shown in FIG. 4.

In this case, the indicators are distinguished by being on different time-frequency resources. Without loss of generality, in the following it is assumed one time-frequency feedback resource associated with each Tx-Rx distance range 301, 302, 303, with indicator #1 or indicator #2 being sent on a feedback resource depending on the above conditions.

Moreover, as the feedback resources 401 and 402 are shared, multiple Target UEs 100 (Rx UEs) may feedback indicator #1 or indicator #2 on a feedback resource. The Tx UE 110 would not be able to distinguish which Rx UEs 100 sent indicator #1 or indicator #2, but this may not be needed for the groupcast power control.

The proposed approach provides implicit information about the Rx UEs’ Tx-Rx distance and SL-RSRPs. Based on the feedback of the Target UE 100 (Rx UEs), on the thresholds of the N Tx-Rx distance ranges, e.g., D ₀ , D ₁ , ... D _N , and the SL-RSRP thresholds R _1, R ₂ , · .. R _n , path- loss (estimates) of the Target UEs 100 (Rx UEs) can be derived for groupcast power control, e.g., based on a path-loss model and/or prior measurements/feedback.

For example, the SL-RSRP threshold Ri 305 for Tx-Rx distance range i 302 can be (pre)configured considering a line-of-sight (LOS) path-loss model and non-LOS (NLOS) path- loss model, e.g., for Tx-Rx distance range t 302, the SL-RSRP threshold Ri 305 can be set based on a LOS path-loss model (or prior measurements) at Tx-Rx distance D _i , i.e., based on the worst case path-loss for a LOS channel from the Source UE 110 (Tx UE) to the Target UE 100 (Rx UE) within the Tx-Rx distance range t 302. Thus, for the Target UE 100 (Rx UE) which feeds back indicator #1 on the feedback resource associated with the Tx-Rx distance range i 302, i.e., a Target UE 100 (Rx UE) with Tx-Rx distance within range i 302 and SL- RSRP > Ri 305, it is very likely that there is a LOS between the Source UE 110 (Tx UE) and the Target UE 100 (Rx UE). Moreover, if one or more Target UEs 100 (Rx UE) send indicator #1 at feedback resource t, a (worst case) path-loss estimate of these Rx UEs 100 can be derived from D _I (upper threshold of range t) and a LOS path-loss model. In a similar way, a (worst case) path-loss estimate of Target UEs 100 (Rx UE) which send indication #2 on the feedback resource associated with Tx-Rx distance range t 302 can be derived, i.e., based on D _I and a NLOS path-loss model. Based on the feedback over all ranges, an estimate of maximum path- loss of all Rx UEs 100 can be derived. Furthermore, based on the feedback message 104, a distribution of the Tx-Rx distance of the Target UEs 100 (Rx UEs) can be obtained which could also be employed for the groupcast power control.

Furthermore, shadowing can be considered to some extent via feedback of indicator #2, i.e., when the SL-RSRP is below a threshold 305 for a given Tx-Rx distance range 301, 302, 303, by configuring the SL-RSRP threshold 305 based on the LOS path-loss and a shadowing model. For example, based on feedback of indicator #2 of a Target UE 100 (Rx UE(s)), the Source UE 110 (Tx UE) can be aware that a Target UE 100 (Rx UE(s)) is below the threshold, e.g., either due to shadowing or a NLOS, and as the aim of groupcast power control is not to compensate the path-loss of each Target UE 100 (Rx UE), this Target UE 100 (Rx UEs)'s path-losses may not be considered for the power control (Note that these path-losses could be considered to some extent depending on the feedback of other Target UEs 100 (Rx UEs) over all ranges).

The SL-RSRP feedback per UE via dedicated feedback resources may enable obtaining the most detailed information about the Rx UEs’ 100 path-losses, but at the expense of increased overhead (scaling with number of Rx UEs 100). Precise path-loss derivation of all Rx UEs 100, however, is not necessary for the groupcast power control, as the goal of the groupcast power control is not to compensate each Rx UE's 100 path-loss. In addition, the groupcast power control can also be dependent and limited by the path-loss between the Tx UE 110 and base station (e.g., gNB). For example, groupcast feedback with shared feedback resources based on ranges may result in smaller overhead, at the expense of obtaining less precise information about the Rx UEs' 100 path-losses. Nevertheless, the use of SL-RSRP ranges leads to several issues as discussed. Moreover, in contrast to SL-RSRP ranges, Tx-Rx distance ranges 301, 302, 303 can be independent of the Tx power used by the Source UE 110 (Tx UE) to send the reference signal. The Tx-Rx distance ranges 301, 302, 303 do not need to be configured by each Tx UE 110 or group, and can be preconfigured by the network, e.g., depending on the service. In addition, the Tx-Rx distance estimate fluctuates less than the RSRP measurements. Also, the Tx-Rx distance can be related to the communication range requirement of services.

Furthermore, with the proposed method based on the Tx-Rx distance ranges 301, 302, 303, it may be possible to enable overhead reduction for the groupcast feedback, with the feedback overhead being independent of the number of Rx UEs 100 in the group. For example, a Target UE 100 (Rx UE) does not need to be configured to send feedback on a specific dedicated resource, e.g., prior unicast connection between the Source UE 110 (Tx UE) and the Target UE 100 (Rx UE) is not required. Moreover, ranges based on the Tx-Rx distance 301, 302, 303 have advantages over using RSRP ranges, as discussed above.

In addition, when the Source UE 100 (Tx UE) changes the transmit power for sending the reference signal, the SL-RSRP threshold for each Tx-Rx distance range may need to be updated. As the difference between the RSRP thresholds for adjacent Tx-Rx distance ranges could be a fixed value, only the change in Tx power needs to be communicated to update the thresholds for each range. This update of the thresholds does not need to be signaled with a high resolution.

Furthermore, it may also be possible to have a single SL-RSRP threshold R for all of the Tx- Rx distance ranges 301, 302, 303. The threshold R can be determined based on minimum RSRP for meeting quality of service (QoS) requirements and/or based on the path-loss between the Source UE 110 (Tx UE) and the gNB, e.g., if the power control is limited by the path-loss to the gNB. In addition, another metric instead of SL-RSRP could be considered for the feedback, e.g., some metric considering also interference.

Moreover, it may also be possible, to perform the discussed method, in an iterative manner based on one threshold or on hierarchical feedback. For example, the Tx-Rx distance ranges can be based on prior information, e.g., from a unicast connection from the Tx UE 110 to the Target UE 100 (Rx UE). The thresholds can also be determined based on the communication range requirement as well as based on the path-loss from the Tx UE 110 to the gNB. Also, the provided method may also support the use of beamforming at the Tx UE 110, e.g., the Tx UE 110 sends reference signals with different beams and then listens for the feedback in the same order as it sent the reference signal on different Tx beams (RACH- like procedure as for the Uu link). The Tx-Rx distance ranges do not need to be configured per beam, but the SL- RSRP thresholds (per range) could be configured per beam. In this case, per beam power control feedback enables beam-based power control.

Reference is made to FIG. 5, which is a schematic view of a flowchart of a method 500 for sending the power control feedback message 104 based on distance ranges.

The method 500 may be performed by the Target UE 100.

At step 501, the Target UE 100 obtains the Tx-Rx distance range where the Tx-Rx distance 101 of the Target UE 100 is within.

Moreover, if the obtained Tx-Rx distance lies within Tx-Rx distance range t 302, the Target UE 100 goes to step 502a at which the Target UE 100 sends indicator on shared feedback resource 1 102. (Here is referred to the Rx UEs as simply UEs). However, if Tx-Rx distance does not lie within a Tx-Rx distance range, the Target UE 100 goes to step 502b at which the Target UE does not send the feedback message 104.

For example, the feedback message 104 from the Target UE 100 (Rx UEs) can also be based solely on the Tx-Rx distance ranges 301, 302, 303, as shown in FIG. 5, where the Target UE 100 (Rx UE) sends feedback to the Source UE 110 (Tx UE) on the feedback resource 102 associated with the Tx-Rx distance range 302 where its Tx-Rx distance 101 lies (is within). This enables the Source UE 110 (Tx UE 110) to obtain a distribution of the Tx-Rx distance of the Target UEs 100 (Rx UEs). This embodiment can be used in conjunction with SL-RSRP ranges, where for a given SL-RSRP range a Rx UE 100 sends feedback also based on the Tx- Rx distance, e.g., on a feedback resource associated with the Tx-Rx distance range in which its Tx-Rx distance lies.

Reference is made to FIG. 6, which is a schematic view of a flowchart of a method 600 for sending the power control feedback message 104 based on the distance ranges and a SL-RSRP threshold. The method 600 may be performed by the Target UE 100.

At step 601, the Target UE 100 obtains the Tx-Rx distance range where the Tx-Rx distance 101 of the Target UE 100 is within.

Moreover, if the obtained Tx-Rx distance lies within Tx-Rx distance range t 302, the Target UE 100 goes to step 602a. (Here is referred to the Target UEs (Rx UEs) as simply UEs). However, if the obtained Tx-Rx distance does not lie within a Tx-Rx distance range, the Target UE 100 goes to step 602b at which the Target UE 100 does not send the feedback message 104.

At step 602a, the Target UE 100 determines whether the SL-RSRP of UE > R. Moreover, if it is determined ‘Ύes” the Target UE 100 goes to step 603a at which the Target UE 100 sends indicator #1 on shared feedback resource i 102. However, if it is determined “No”, the Target UE 100 goes to step 603b and sends indicator #2 on shared feedback resource i 102 (optional step).

For example, the discussed method may be based on a single SL-RSRP threshold R over all ranges as described in the flowchart depicted FIG. 6. The threshold R can be determined based on the minimum RSRP for meeting QoS requirements and/or based on the path-loss between the Tx UE 100 and the gNB. If the SL-RSRP of a Target UE 100 is above a (pre)configured threshold R, the Target UE 100 sends indicator #1 on the feedback resource associated with the Tx-Rx distance range in which its Tx-Rx distance lies. The feedback is sent to the Source UE 110 (Tx UE). If the SL-RSRP of a Target UE 100 is less than or equal to the (pre)configured threshold R, the Target UE 100 can send indicator #2 on the feedback resource associated with the Tx-Rx distance range in which its Tx-Rx distance lies. As QoS requirements of Rx UEs with SL-RSRP below a threshold may not be able to be guaranteed via power control, the feedback of indicator #2 can be optional as depicted in FIG. 6.

Reference is made to FIG. 7, which is a schematic view of a flowchart of a method 700 including one SL-RSRP threshold per each distance range.

The method 700 may be performed by the Target UE 100. At step 701, the Target UE 100 obtains the Tx-Rx distance range where the Tx-Rx distance 101 of the Target UE 100 is within.

Moreover, if the obtained Tx-Rx distance lies within Tx-Rx distance range i 302, the Target UE 100 goes to step 702a. (Here is referred to the Target UEs (Rx UEs) as simply UEs). However, if the obtained Tx-Rx distance does not lie within a Tx-Rx distance range, the Target UE 100 goes to step 702b at which the Target UE 100 does not send the feedback message 104.

At step 702a, the Target UE 100 determines whether the SL-RSRP of UE > R _i . Moreover, if it is determined ‘Ύes” the Target UE 100 goes to step 703a at which the Target UE 100 sends indicator #1 on shared feedback resource 1 102. However, if it is determined “No”, the Target UE 100 goes to step 703b and sends indicator #2 on shared feedback resource i 102 (optional step). For example, in the above method 700 depicted in FIG. 7, on the feedback resource associated with the Tx-Rx distance range that the Tx-Rx distance of the Target UE is within (e.g., Tx-Rx distance range t ) the Target UE 100 sends indicator #1 if its SL-RSRP is above the (pre)configured SL-RSRP threshold Ri of the Tx-Rx distance range t. (Here is referred to the Target UEs (Rx UEs) as simply UEs). The feedback is sent to the Source UE 110 (Tx UE 110). If the SL-RSRP of the Target UE 100, located within Tx-Rx distance range t, is less than or equal to the SL-RSRP threshold R _i , the Target UE 100 sends indicator #2 on the feedback resource associated with the Tx-Rx distance range t. As before, the feedback of indicator #2 can be considered optional. In the above method, only one SL-RSRP threshold per distance range is considered. In general, however, multiple SL-RSRP thresholds may be considered for each distance range.

Reference is made to FIG. 8, which is a schematic view of selecting the feedback resource when having only one Tx-Rx distance range 302 with distances less than or equal to a Tx-Rx distance threshold D ₁ and with a SL-RSRP threshold R ₁ .

The threshold D ₁ could be determined based on the communication range requirement of a given service. If the Tx-Rx distance of a Target UE 100 (Rx UE) is less than or equal to D _1, the Target UE 100 (Rx UE) sends indicator #1 if its SL-RSP is above R ₁ . Optionally, if the SL- RSRP is less than or equal to R _1, the Target UE 100 (Rx UE) sends indicator #2 (assuming the Tx-Rx distance of the Target UE 100 (Rx UE) is less than or equal to D ₁ ). If the Tx-Rx distance of the Target UE 100 (Rx UE) is larger than D _1, it does not send any feedback.

References are made from FIG. 9a and FIG. 9b, which are schematic views of sending a successive power control feedback message.

The successive power control feedback message may be sent based on iterative and hierarchical feedback. For example, starting with two Tx-Rx distance ranges 301, 302 determined by D ₀ , D ₁ and D ₂ as depicted in FIG. 9a, along with two SL-RSRP thresholds and R ₂ , for range 1 and range 2, respectively. After the feedback of the Target UEs 100 (Rx UEs) on two feedback resources 102, 304 (one for range 1 and another for range 2), a more precise determination of the path-losses of the Target UEs 100 (Rx UEs) can be obtained with successive feedback rounds, e.g., by splitting a determined distance range 301 from a previous feedback round into two or more ranges 901, 902 (i.e., with one or more further Tx-Rx distance thresholds which are communicated to the Target UEs 100 (the Rx UEs), as can be derived from FIG. 9b. For example, based on feedback message 104 in a first feedback round, the range 1 301 may be split into two ranges, i.e., the range 3 901 and the range 4 902, based on threshold D ₃ as depicted in FIG. 9b. For the second round of feedback, the Target UEs 100 (Rx UEs) feedback based on range 3 901 and range 4902 over two feedback resources 903, 904, as well as based on additional SL-RSRP thresholds R ₃ and R ₄ for range 3901 and range 4902, respectively. As the Tx-Rx distance ranges in the second feedback round are narrower, the Source UE 110 (Tx UE) can derive a better estimation of the path-loss of the Target UE 100 (Rx UE), as compared with the first feedback round. After the successive feedback round, the Target UEs within distance range 1 have provided feedback also based on one or more SL-RSRP thresholds for this distance range, i.e. based on R ₁ R ₂ , R ₃ and R ₄ .

Although the implicit feedback is discussed here, explicit feedback of SL-RSRP from UE(s) could also be considered for a certain Tx-Rx distance range, in particular for iterative feedback schemes or when the Tx UE 110 is aware that there is only one Rx UE 100 in a given Tx-Rx distance range. As described before, successive feedback rounds can be performed by splitting a Tx-Rx distance range and/or in addition, requesting explicit SL-RSRP feedback from certain UEs, e.g., UEs which previously indicated an SL-RSRP below a threshold in a Tx-Rx distance range from a previous feedback round.

In the proposed schemes, the SL-RSRP can be replaced by another figure of merit, e.g., Reference Signal Received Quality (RSRQ) or a measurement considering interference in the sidelink, e.g., to enable power control to consider interference.

Moreover, the conditions for sending the feedback for a given Tx-Rx distance range could also be based on multiple SL-RSRP thresholds. In this case, more than two indicators could also be considered for the feedback, each one associated with different conditions for the measured SL- RSRP of the Rx UE with respect to the multiple SL-RSRP thresholds.

FIG. 10 shows a method 1000 for a Target UE 100, according to an embodiment ofthe invention. The method 1000 may be carried out by the Target UE 100, as it described above.

The method 1000 comprises a step 1001 of obtaining, a distance 101 between the Target UE 100 and a Source UE 110.

The method 1000 further comprises a step 1002 of selecting a feedback resource 102 depending on whether the obtained distance 101 is below, above or equal to one or more distance thresholds 103.

The method 1000 further comprises a step 1003 of sending a power control feedback message 104 to the Source UE 110 on the selected feedback resource 102.

FIG. 11 shows a method 1100 for a Source UE 110, according to an embodiment of the invention. The method 1100 may be carried out by the Source UE 110, as it described above.

The method 1100 comprises a step 1101 of sending a transmission 201 to two or more Target UEs 100.

The method 1100 further comprises a step 1102 of receiving, from at least one Target UE 100, a respective power control feedback message 104 on at least one feedback resource 102 depending on whether an obtained distance 101 from the Source UE 110 to the at least one Target UE 100 is below, above or equal to one or more distance thresholds 103.

The present invention has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed invention, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.