Apparatus and method for SL data transmission for unicast sidelink between user equipments

Abstract

An ARQ system for sidelink communication between a transmitter and a receiver with the help of a cooperative UE or a relay UE is disclosed. The relay intercepts the initial transmission from the transmitter to the receiver. If the relay does not intercept any ARQ feedback from the receiver (DTX), it retransmits the initial transmission. Upon receiving at least sidelink control information SCI identifying the retransmission, the transmitter terminates the HARQ process, assuming that the relay is now responsible for the retransmission. Upon receiving the retransmission, the receiver feeds back a HARQ ACK to the relay and the transmitter. If the receiver correctly receives the initial transmission, it feeds back a HARQ ACK to the relay and the transmitter, and both the relay and the transmitter stop the HARQ process. If the relay does not successfully receive the initial transmission, it feeds back a NACK to the transmitter, which performs the retransmission to the relay.

Description

Technical Field

[0001] The following disclosure relates to the field of sidelinks, or more specifically, to systems, apparatuses, and methods for sidelink data transmission for unicast sidelinks between user equipment (e.g., Tx UE (UE: User Equipment; Tx UE: Transmitter UE) and Rx UE (Rx UE: Receiver UE)). Specifically, the present disclosure is directed to UE-to-UE relay based on 3GPP Sidelink (SL) in Rel'17 and later versions. Background Art

[0002] SL-based UE-to-UE relay is part of Rel'17 SI SP-190443 led by SA2 and RP-193253 led by RAN2.

[0003] So far, SL-based UE-to-UE relay has not been specified in the 3GPP standards.

[0004] TS 38.300 provides a description of NR PC5 and NR PC5-based SL communications between neighboring UEs for both in-coverage (IC) and out-of-coverage (OoC) operations.

[0005] PC5-based SL communication is based on a transmitter, such as a Tx UE, which is oriented towards a one-to-many broadcast principle, where a receiver (e.g., Rx UE) needs to monitor SL reception through one or more (pre-)configured resource pools, regardless of whether the SL transmission is for unicast, groupcast, or broadcast. The ID of the Tx UE, referred to as the source ID (SRC ID), and the ID of the receiver, referred to as the destination ID (DST ID), are partly included in the SL control information (SCI) sent by the Tx UE to schedule the SL transmission of a transport block (TB), and partly included in the header of the MAC PDU within the TB. The Rx UE needs to monitor to receive the SCI and TB through (multiple) (pre-)configured resource pools, and filter out the one for the Rx UE based on the received DSTID.

[0006] NR SL supports Hybrid Automatic Repeat Request (HARQ) with feedback, with only NACK (Negative Acknowledgement) as Opt-1 or ACK (Positive Acknowledgement) / NACK as Opt-2 for multicast SL between a Tx UE and a group of Rx UEs, and as Opt-2 for unicast SL between a Tx UE and a group of Rx UEs.

[0007] NR SL also supports some operations related to SL Radio Link Failure (RLF) for unicast SL, including SL RLF detection by Tx UE. Service continuity and SL RLF recovery are not supported.

[0008] The first studies on supporting SL-based UE-to-UE relaying have just started in 3GPP. So far, there has been no contribution in RAN# to enhance SL communication for SL-based UE-to-UE relaying. Summary of the Invention

[0009] It is desirable to provide a SL-based UE-to-UE relay that can exhibit one or more of the following characteristics:

[0010] -Relay based on single-hop NR sidechain,

[0011] - low or minimal specification impact,

[0012] - good service continuity,

[0013] - impact on the user plane protocol stack and control plane procedures (e.g. connection management of relay connections),

[0014] - Assuming no new physical layer channels / signals.

[0015] A possible use case scenario for this desired SL-based UE-to-UE relay includes a transmitter (e.g., Tx UE), a receiver (e.g., Rx UE), and a relay device (e.g., R-UE (R-UE: Relay UE)). In this scenario, the Tx UE uses SL-based UE-to-UE relay via the relay device R-UE to transmit SL data to the Rx UE, because the direct SL between the Tx UE and the Rx UE is currently suffering from, for example, poor sidelink radio conditions or even SL RLF. It is assumed that an authorized appropriate R-UE has been discovered and selected to assist the communication between the Tx UE and the Rx UE, and the detailed establishment process is not the focus of the embodiments of the present disclosure.

[0016] One objective of the exemplary embodiments is, inter alia, to enable and facilitate SL data transmission between a Tx UE and a Rx UE using SL-based UE-to-UE relaying via an R-UE, while allowing the Tx UE and the Rx UE to quickly and efficiently return from UE-to-UE relay mode to direct SL mode (i.e., direct communication between the Tx UE and the Rx UE without the use of a relay) in a seamless manner once direct SL mode is applicable again, with minimal impact on the current SL standard.

[0017] Furthermore, exemplary embodiments are intended to achieve, among other things, one or both of the following objectives:

[0018] (i) facilitating SL data transmission of unicast SL between Tx UE and Rx UE using SL-based UE-to-UE relay via R-UE; and

[0019] (ii) Once direct SL mode is applicable again for unicast SL of Tx UE and Rx UE, seamless return from current UE-to-UE relay mode to direct SL mode is achieved and facilitated.

[0020] According to a first exemplary aspect of the present disclosure, a method is disclosed, the method comprising:

[0021] - transmitting at least one HARQ transmission of a sidelink transport block, the at least one HARQ transmission comprising destination identifier information indicating a destination identifier of a receiver,

[0022] - monitoring receiver HARQ feedback for at least one HARQ transmission from a receiver to obtain a receiver HARQ feedback monitoring result,

[0023] - monitoring relay HARQ feedback for at least one HARQ transmission from a relay device to obtain a relay HARQ feedback monitoring result, and

[0024] - Determining a retransmission decision regarding whether to transmit at least one HARQ retransmission of the sidelink transport block based on the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result.

[0025] The at least one HARQ transmission may be the first HARQ transmission of the sidelink transport block, in particular the first HARQ transmission of a plurality of consecutive HARQ transmissions of the sidelink transport block.

[0026] The receiver HARQ feedback may specifically be a positive acknowledgement (eg ACK) or a negative acknowledgement (eg NACK). Furthermore, receiver HARQ feedback indicating discontinuous transmission (eg DTX (discontinuous transmission)) may not be received.

[0027] The relay HARQ feedback may specifically be a negative acknowledgement, such as a NACK. Furthermore, receiver HARQ feedback indicating discontinuous transmission (e.g., DTX) may not have been received. Generally, the relay HARQ feedback may also be a positive acknowledgement, such as an ACK, particularly for a HARQ transmission different from the at least one HARQ transmission, such as a HARQ retransmission.

[0028] Monitoring of receiver HARQ feedback for at least one HARQ transmission from the receiver may comprise receiving receiver HARQ feedback for at least one HARQ transmission (particularly indicating a positive or negative acknowledgement), or not receiving receiver HARQ feedback for at least one HARQ transmission, for example within a specified time period, for example after transmitting at least one HARQ transmission indicating discontinuous transmission.

[0029] Monitoring of relay HARQ feedback for at least one HARQ transmission from a relay device may include: receiving relay HARQ feedback for at least one HARQ transmission (in particular indicating a negative acknowledgement), or, for example, not receiving relay HARQ feedback for at least one HARQ transmission within a specified time period, for example after transmitting at least one HARQ transmission indicating discontinuous transmission.

[0030] Specifically, if a receiver HARQ feedback indicating a positive acknowledgment is received during the monitoring period, the receiver HARQ feedback monitoring result may indicate a positive acknowledgment. Furthermore, if a receiver HARQ feedback indicating a negative acknowledgment is received during the monitoring period, the receiver HARQ feedback monitoring result may indicate a negative acknowledgment. Furthermore, if a receiver HARQ feedback indicating a positive or negative acknowledgment is not received during the monitoring period, the receiver HARQ feedback monitoring result may indicate discontinuous transmission.

[0031] Specifically, if relay HARQ feedback indicating a positive acknowledgment is received during the monitoring period, the relay HARQ feedback monitoring result may indicate a positive acknowledgment. Furthermore, if relay HARQ feedback indicating a negative acknowledgment is received during the monitoring period, the relay HARQ feedback monitoring result may indicate a negative acknowledgment. Furthermore, if no relay HARQ feedback indicating a positive or negative acknowledgment is received during the monitoring period, the relay HARQ feedback monitoring result may indicate discontinuous transmission.

[0032] For example, determining the retransmission decision may include one or more of the following:

[0033] - determining whether a predefined condition for the retransmission decision (e.g., a condition within an if clause, etc.) is satisfied, for example, by evaluating a logical expression based on the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result (in this case, the retransmission decision may or may not be stored in a variable);

[0034] - Determining a value of a retransmission decision variable (eg, a Boolean variable) indicating a retransmission decision, for example, by evaluating a logical expression based on a receiver HARQ feedback monitoring result and a relay HARQ feedback monitoring result.

[0035] For example, transmitting at least one HARQ retransmission may be determined as a retransmission decision. For example, this retransmission decision may be referred to as "Retransmission!". Furthermore, not transmitting at least one HARQ retransmission may be determined as a retransmission decision. For example, this retransmission decision may be referred to as "No retransmission!". The terms "Retransmission!" and "No retransmission!" are used herein for illustrative purposes only and are not limiting. For example, "TRUE" or "yes" may be used instead of "Retransmission!", and "FALSE" or "no" may be used instead of "No transmission!".

[0036] With the above-described method, SL data transmission between a transmitter and a receiver may be facilitated using SL-based UE-to-UE relaying, for example, via a relay device.

[0037] The method may be executed and / or controlled, for example, by a mobile device (e.g., an automated Internet of Things (IoT) device and / or a user equipment (UE)). For example, the method may be executed and / or controlled using at least one processor of the mobile device.

[0038] The mobile communication network may be, for example, a cellular network. The mobile communication network may be, for example, a mobile phone network such as 2G / 3G / 4G / 5G / New Radio (NR) and / or future cellular communication networks. The 2G / 3G / 4G / 5G / NR cellular radio communication standards are developed by 3GPP and are currently available at http: / / www.3gpp.org / .

[0039] According to another exemplary aspect of the present invention, a computer program is disclosed which, when executed by a processor, causes an apparatus (eg, a server) to perform and / or control the actions of the method according to the first exemplary aspect.

[0040] The computer program may be stored on a computer-readable storage medium, in particular a tangible and / or non-transitory medium. The computer-readable storage medium may be, for example, a disk or a memory. The computer program may be stored on the computer-readable storage medium in the form of instructions encoding the computer-readable storage medium. The computer-readable storage medium may be used to participate in the operation of a device, such as an internal or external memory, such as a read-only memory (ROM) or a hard disk of a computer, or for distribution of the program, such as an optical disk.

[0041] According to another exemplary aspect of the present disclosure, a device is disclosed. The device is configured to execute and / or control the method according to the first exemplary aspect, or includes corresponding components for executing and / or controlling the method according to the first exemplary aspect.

[0042] The components of the device can be implemented in hardware and / or software. They may include, for example, at least one processor for executing a computer program code for performing the above-mentioned functions, at least one memory for storing program code, or both. Alternatively, they may include, for example, a circuit system designed to implement the above-mentioned functions, such as implemented in a chipset or chip, such as an integrated circuit. Typically, the component may include, for example, one or more processing components or processors.

[0043] According to another exemplary aspect of the present disclosure, a device is disclosed, which includes at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, together with the at least one processor, cause the device (e.g., the above-mentioned device) to at least execute and / or control the method according to the first exemplary aspect.

[0044] The above-disclosed apparatus according to any aspect of the present disclosure may be a module or component for a device, such as a chip. Alternatively, the disclosed apparatus according to any aspect of the present disclosure may be a device, such as a server or a server cloud. The disclosed apparatus according to any aspect of the present disclosure may include only the disclosed components, such as a part, a processor, a memory, or may further include one or more additional components.

[0045] As used herein, such a device (e.g., a mobile device) can, for example, be portable (e.g., weighing less than 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1 kg or less), such as a mobile phone, a personal digital assistant, a computer, a laptop computer, as non-limiting examples. The device can, for example, include or be connectable to a display for displaying information, such as pictures or videos transmitted to the device via a mobile communication network, to name just one non-limiting example. The device can, for example, include or be connectable to means for outputting sound, such as in the form of spoken commands or information.

[0046] According to a second exemplary aspect of the present disclosure, a method is disclosed, the method comprising:

[0047] - receiving at least one HARQ transmission of a sidelink transport block from a transmitter, the at least one HARQ transmission including destination identifier information indicating a destination identifier of a receiver (e.g., Rx UE), and

[0048] - In case at least one HARQ transmission has been successfully received, at least

[0049] - monitoring receiver HARQ feedback for at least one HARQ transmission from a receiver to obtain a receiver HARQ feedback monitoring result, and

[0050] - Determining a relay decision as to whether data of at least one HARQ transmission needs to be relayed to the receiver based on the receiver HARQ feedback monitoring result.

[0051] The at least one HARQ transmission may be the first HARQ transmission of the sidelink transport block, in particular the first HARQ transmission of a plurality of consecutive HARQ transmissions of the sidelink transport block.

[0052] In particular, the HARQ transmission may be received successfully or unsuccessfully. For example, unsuccessfully receiving the HARQ transmission may include receiving only a portion of the HARQ transmission, such as sidelink control information (SCI) used to schedule the HARQ transmission, and / or receiving the HARQ transmission with errors, and / or receiving the HARQ transmission with uncorrectable errors.

[0053] The monitoring of receiver HARQ feedback and the determination of the relay decision are performed at least when the at least one HARQ transmission has been successfully received. The monitoring of receiver HARQ feedback can be based on, for example, information received in the at least one HARQ transmission, such as sidelink control information (SCI) used to schedule the at least one HARQ transmission, or can be implemented by such information.

[0054] Specifically, monitoring of receiver HARQ feedback may include:

[0055] - deriving a HARQ feedback channel for a receiver (e.g., Rx UE) based on the received SCI of at least one HARQ transmission,

[0056] Monitoring receiver HARQ feedback from the receiver on the derived HARQ feedback channel. Monitoring receiver HARQ feedback and determining a relay decision can also be performed, for example, when a HARQ transmission was received but not successfully (e.g., only partially or with errors). Monitoring receiver HARQ feedback and determining a relay decision can also be performed, for example, without prior verification of whether the received HARQ transmission was successfully received.

[0057] The receiver HARQ feedback may specifically be a positive acknowledgement (eg, ACK) or a negative acknowledgement (eg, NACK). Furthermore, the receiver HARQ feedback may not be received, which indicates discontinuous transmission (eg, DTX).

[0058] Monitoring of receiver HARQ feedback for at least one HARQ transmission from the receiver may include receiving receiver HARQ feedback for at least one HARQ transmission (particularly indicating a positive or negative acknowledgement), or not receiving receiver HARQ feedback for at least one HARQ transmission, for example within a specified time period (e.g. within a specified time period after transmitting at least one HARQ transmission), which indicates discontinuous transmission.

[0059] Specifically, if a receiver HARQ feedback indicating a positive acknowledgment is received during the monitoring period, the receiver HARQ feedback monitoring result may indicate a positive acknowledgment. Furthermore, if a receiver HARQ feedback indicating a negative acknowledgment is received during the monitoring period, the receiver HARQ feedback monitoring result may indicate a negative acknowledgment. Furthermore, if a receiver HARQ feedback indicating a positive or negative acknowledgment is not received during the monitoring period, the receiver HARQ feedback monitoring result may indicate discontinuous transmission.

[0060] For example, determining a relay decision may include one or more of the following:

[0061] - Determining whether a predefined condition for the relay decision (e.g., a condition within an if clause, etc.) is satisfied, for example, by evaluating a logical expression based on the receiver HARQ feedback monitoring result (in this case, the retransmission decision may or may not be stored in a variable);

[0062] - Determining the value of a relay decision variable (eg, a Boolean variable) indicating the relay decision, for example, by evaluating a logical expression based on the receiver HARQ feedback monitoring results.

[0063] For example, transmitting at least one HARQ retransmission can be determined as a retransmission decision. For example, this retransmission decision can be referred to as "Relay!". Furthermore, not transmitting at least one HARQ retransmission can be determined as a retransmission decision. For example, this retransmission decision can be referred to as "No relay!". The terms "Relay!" and "No relay!" are used herein for illustrative purposes only and are not limiting. For example, "TRUE" or "yes" can be used instead of "Relay!", and "FALSE" or "no" can be used instead of "No relay!".

[0064] The data of at least one HARQ transmission may include, for example, SL data or TB in such a TB.

[0065] With the above-described method, SL data transmission between a transmitter and a receiver may be facilitated using SL-based UE-to-UE relaying, for example, via a relay device.

[0066] The method may be executed and / or controlled, for example, by a mobile device (e.g., an automated Internet of Things (IoT) device and / or a user equipment (UE)). For example, the method may be executed and / or controlled using at least one processor of the mobile device.

[0067] According to another exemplary aspect of the present disclosure, a computer program is disclosed which, when executed by a processor, causes an apparatus (eg, a server) to perform and / or control actions of the method according to the second exemplary aspect.

[0068] The computer program may be stored on a computer-readable storage medium, in particular a tangible and / or non-transitory medium. The computer-readable storage medium may be, for example, a disk or a memory. The computer program may be stored on the computer-readable storage medium in the form of instructions encoding the computer-readable storage medium. The computer-readable storage medium may be used to participate in the operation of a device, such as an internal or external memory, such as a read-only memory (ROM) or a hard disk of a computer, or for distribution of the program, such as an optical disk.

[0069] According to another exemplary aspect of the present disclosure, a device is disclosed. The device is configured to execute and / or control the method according to the second exemplary aspect, or includes corresponding components for executing and / or controlling the method according to the second exemplary aspect.

[0070] The components of the device can be implemented in hardware and / or software. They may include, for example, at least one processor for executing a computer program code for performing the required function, at least one memory for storing program code, or both. Alternatively, they may include, for example, a circuit system designed to implement the required function, such as implemented in a chipset or chip, such as an integrated circuit. Typically, the component may include, for example, one or more processing components or processors.

[0071] According to another exemplary aspect of the present disclosure, a device is disclosed, which includes at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, together with the at least one processor, cause the device (e.g., the above-mentioned device) to at least execute and / or control the method according to the second exemplary aspect.

[0072] The above-disclosed apparatus according to any aspect of the present disclosure may be a module or component for a device, such as a chip. Alternatively, the disclosed apparatus according to any aspect of the present disclosure may be a device, such as a server or a server cloud. The disclosed apparatus according to any aspect of the present disclosure may include only the disclosed components, such as a part, a processor, or a memory, or may further include one or more additional components.

[0073] According to another exemplary aspect of the present disclosure, a system is disclosed, the system comprising:

[0074] At least one apparatus according to the first exemplary aspect above and at least one apparatus according to the second exemplary aspect above.

[0075] Utilizing the aspects of the present disclosure described above, SL data transmission of a unicast sidelink between a transmitter (eg, Tx UE) and a receiver (eg, Rx UE) may be facilitated.

[0076] Hereinafter, exemplary features and exemplary embodiments of all aspects of the present disclosure will be described in further detail.

[0077] According to an exemplary embodiment of the first exemplary aspect, the method further comprises:

[0078] - Transmitting at least one HARQ retransmission according to the retransmission decision.

[0079] Specifically, if the retransmission decision is "Retransmission!", transmission of at least one HARQ retransmission may be performed, and if the retransmission decision is "No retransmission!", transmission of at least one HARQ retransmission may be deferred.

[0080] According to another exemplary embodiment of the first exemplary aspect, the HARQ retransmission includes destination identifier information indicating a destination identifier of the relay. In this way, the transmitter can directly address the relay device, for example, via the HARQ retransmission, so that the relay device can relay the HARQ retransmission to the receiver.

[0081] According to another exemplary embodiment of the first exemplary aspect, determining the retransmission decision includes:

[0082] - determining to transmit at least one HARQ retransmission at least in a case where the receiver HARQ feedback monitoring result indicates discontinuous transmission (eg, HARQ DTX) and the relay HARQ feedback monitoring result indicates negative acknowledgement (eg, HARQ NACK).

[0083] For example, a receiver HARQ feedback monitoring result indicating discontinuous transmission may indicate that the receiver has not received the HARQ transmission, and thus, for example, relaying via a relay device is desired. Furthermore, a relay HARQ feedback monitoring result indicating a negative acknowledgement may indicate that the relay device has received the HARQ transmission, but unsuccessfully (e.g., only partially or with errors). In this case, the retransmission decision may be determined as "Retransmission!", so that, for example, the retransmission may be performed, and the relay device may successfully receive the retransmission and perform relaying.

[0084] According to another exemplary embodiment of the first exemplary aspect, transmitting at least one HARQ transmission comprises:

[0085] - Transmitting at least one HARQ transmission as a multicast sidelink HARQ transmission (eg, as a multicast sidelink HARQ Opt-2 transmission).

[0086] In this way, at least one HARQ transmission may address both a receiver and, for example, a relay device.

[0087] The at least one HARQ transmission may comprise destination group identifier information, eg indicating a destination group identifier of the destination group.The destination group may in particular comprise a receiver and at least one relay device.

[0088] According to an exemplary embodiment, the destination identifier of the receiver can be used as a destination group identifier. In this case, the destination identifier information indicating the destination identifier of the receiver can also be used as the destination group identifier information indicating the destination group identifier, so that, for example, no additional destination group identifier information is required. The destination identifier used as the destination group identifier is known to at least the transmitter (e.g., Tx UE) and the relay device (e.g., R-UE). The receiver (e.g., Rx UE) may or may not know that at least one HARQ transmission is multicast and / or that the destination identifier is also used as the destination group identifier because the receiver knows that at least one transmission is addressed to it based on the destination identifier. Therefore, the relay can be visible to the receiver (as in the former case) or invisible to the receiver (as in the latter case).

[0089] According to another exemplary embodiment of the first exemplary aspect, transmitting at least one HARQ retransmission comprises:

[0090] - Transmitting at least one HARQ retransmission as a unicast sidelink HARQ (re)transmission.

[0091] In this way, at least one HARQ retransmission may be directly addressed to the relay device.

[0092] The at least one HARQ retransmission may specifically include destination identifier information indicating a destination identifier of the relay device.

[0093] According to another exemplary embodiment of the first exemplary aspect, determining the retransmission decision includes:

[0094] - In a case where the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate a negative acknowledgement (eg, HARQ NACK), determining that at least one HARQ retransmission needs to be transmitted.

[0095] For example, a receiver HARQ feedback monitoring result indicating a negative acknowledgement may indicate that the receiver has received the HARQ transmission, but unsuccessfully (e.g., only partially or with errors), and thus, for example, relaying via a relay device is desired. Furthermore, for example, a relay HARQ feedback monitoring result indicating a negative acknowledgement may indicate that the relay device has received the HARQ transmission, but unsuccessfully (e.g., only partially or with errors). In this case, the retransmission decision may be determined as "Retransmission!", so that, for example, the retransmission may be performed, and the relay device may successfully receive the retransmission and perform relaying.

[0096] For example, a receiver HARQ feedback monitoring result indicating a negative acknowledgement may further indicate that the receiver has become reachable to the transmitter, especially in the case of an earlier receiver HARQ feedback monitoring result indicating discontinuous transmission. Thus, a return to direct SL mode may be made between the receiver and the transmitter.

[0097] According to another exemplary embodiment of the first exemplary aspect, determining the retransmission decision includes:

[0098] - In a case where the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate discontinuous transmission (eg, HARQ DTX), determining that at least one HARQ retransmission does not need to be transmitted.

[0099] For example, a receiver HARQ feedback monitoring result indicating discontinuous transmission may indicate that the receiver is unable to receive the HARQ transmission, and thus, for example, desires to relay via a relay device. In addition, for example, a relay HARQ feedback monitoring result indicating discontinuous transmission may indicate that the relay device (particularly according to the second exemplary aspect) has successfully received at least the first HARQ transmission, and thus no retransmission is required.

[0100] By using DTX instead of ACK to inform the transmitter of reception, in particular successful reception, of at least one HARQ transmission, the relay device can better monitor the receiver HARQ feedback because the relay device is not occupied with sending ACKs.

[0101] According to another exemplary embodiment of the first exemplary aspect, the method further comprises:

[0102] -Terminate the HARQ process.

[0103] Specifically, the method may include:

[0104] - In a case where the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate discontinuous transmission (eg, HARQ DTX), terminating the HARQ process.

[0105] For example, a receiver HARQ feedback monitoring result indicating discontinuous transmission may indicate that the receiver is unable to receive the HARQ transmission, and thus, for example, relaying via a relay device is desired. In addition, for example, relay HARQ feedback indicating discontinuous transmission may indicate that the relay device (particularly according to the second exemplary aspect) has successfully received the HARQ transmission and it is expected that, for example, the relay device relays data from the HARQ transmission to the receiver, so that the HARQ process may terminate.

[0106] Terminating the HARQ process may be performed with or without detecting that the relay device is relaying data to the receiver.

[0107] According to another exemplary embodiment of the first exemplary aspect, determining the retransmission decision includes:

[0108] - In a case where the receiver HARQ feedback monitoring result indicates negative acknowledgement (eg, HARQ NACK) and the relay HARQ feedback monitoring result indicates discontinuous transmission (eg, HARQ DTX), determining not to transmit at least one HARQ retransmission.

[0109] For example, a receiver HARQ feedback monitoring result indicating a negative acknowledgement may indicate that the receiver has received the HARQ transmission, but unsuccessfully (e.g., only partially or with errors), such that relaying via a relay device is desired, for example. Furthermore, a relay HARQ feedback monitoring result indicating discontinuous transmission may indicate that the relay device (particularly according to the second exemplary aspect) has successfully received the HARQ transmission, such that retransmission is not required, for example.

[0110] According to another exemplary embodiment of the first exemplary aspect, the method further comprises:

[0111] - In a case where the receiver HARQ feedback monitoring result indicates negative acknowledgement (eg, HARQ NACK) and the relay HARQ feedback monitoring result indicates discontinuous transmission (eg, HARQ DTX), terminating the HARQ process.

[0112] For example, a receiver HARQ feedback monitoring result indicating a negative acknowledgement may indicate that the receiver has received the HARQ transmission, but not successfully (e.g., only partially or with errors), such that relaying via a relay device is desired, for example. Furthermore, a relay HARQ feedback monitoring result indicating discontinuous transmission may indicate that the relay device (particularly according to the second exemplary aspect) has successfully received the HARQ transmission and that it is expected, for example, that the relay device relays data from the HARQ transmission to the receiver, such that the HARQ process may terminate.

[0113] Terminating the HARQ process may be performed with or without detecting that the relay device is relaying data to the receiver.

[0114] For example, a receiver HARQ feedback monitoring result indicating a negative acknowledgement may further indicate that the receiver has become reachable to the transmitter, especially in the case of an earlier receiver HARQ feedback monitoring result indicating discontinuous transmission. Thus, a return to direct SL mode may be made between the receiver and the transmitter.

[0115] According to another exemplary embodiment of the first exemplary aspect, determining the retransmission decision includes:

[0116] - In case the receiver HARQ feedback monitoring result indicates a positive acknowledgement (eg, HARQ ACK), determining that at least one HARQ retransmission does not need to be transmitted.

[0117] For example, a receiver HARQ feedback monitoring result indicating a positive acknowledgement may indicate that the receiver can successfully receive the HARQ transmission, thereby, for example, not requiring relaying via a relay device and / or not requiring retransmission. Specifically, the transmitter may return to direct SL mode with or without releasing the relay device.

[0118] According to another exemplary embodiment of the first exemplary aspect, the method further comprises:

[0119] - In case the receiver HARQ feedback monitoring result indicates a positive acknowledgement (eg, HARQ ACK), terminating the HARQ process.

[0120] For example, a receiver HARQ feedback monitoring result indicating a positive acknowledgement may indicate that the receiver can successfully receive the HARQ transmission, such that, for example, no transmission needs to be relayed via a relay device and / or no retransmission is required.

[0121] According to another exemplary embodiment of the first exemplary aspect, the method further comprises:

[0122] - Release the relay device.

[0123] Specifically, the method may further include releasing the relay device according to the receiver HARQ feedback monitoring result. For example, if the receiver HARQ feedback monitoring result indicates a positive acknowledgement, the relay device may be released.

[0124] According to a further exemplary embodiment of the first exemplary aspect, the at least one HARQ transmission of the sidelink transport block is a first HARQ transmission of the sidelink transport block, in particular a first HARQ transmission of more than one, eg consecutive, HARQ transmissions of the sidelink transport block.

[0125] According to another exemplary embodiment of the first exemplary aspect, the method further comprises:

[0126] - transmit more than one consecutive HARQ transmission of a sidelink transport block,

[0127] - monitoring corresponding receiver HARQ feedback for corresponding HARQ transmission from the receiver to obtain corresponding receiver HARQ feedback monitoring results,

[0128] - monitoring the corresponding relay HARQ feedback for the corresponding HARQ transmission from the relay device to obtain the corresponding relay HARQ feedback monitoring result,

[0129] - determining a corresponding retransmission decision regarding whether at least one corresponding HARQ retransmission of the sidelink transport block needs to be transmitted based on the corresponding receiver HARQ feedback monitoring result and the corresponding relay HARQ feedback monitoring result.

[0130] More than one consecutive HARQ (re)transmission including the first HARQ transmission of a TB may be transmitted by the transmitter, for example, using enhanced SL HARQ Opt-2 to ensure the purpose (i.e., expecting the relay device to successfully receive the TB). That is, for all these HARQ (re)transmissions, the transmitter may detect / receive DTX from the relay device and NACK / DTX from the receiver before terminating the HARQ process.

[0131] According to a further exemplary embodiment of the first exemplary aspect, the more than one consecutive HARQ transmissions of the sidelink transport block comprise a first HARQ transmission of the sidelink transport block.

[0132] According to another exemplary embodiment of the first exemplary aspect, the method further comprises:

[0133] - monitoring a message including sidelink control information (SCI) from a relay device to a receiver to obtain an SCI monitoring result,

[0134] - Optionally, a termination decision on whether the HARQ process needs to be terminated is determined according to the SCI monitoring result.

[0135] For example, the transmitter may monitor at least the SCI sent by the relay to the receiver, wherein the SCI may be used by the relay to schedule data transmission to the receiver to ensure that the relay is receiving data from the transmitter and relaying the data to the receiver. This monitoring may be used, for example, by the transmitter to determine whether to terminate the HARQ process.

[0136] Terminating the HARQ process may specifically comprise terminating any transmission of a HARQ transmission or retransmission of a (current) sidelink transport block.

[0137] For example, a determination of termination may include one or more of the following:

[0138] - determining whether a predefined condition for the termination decision (e.g., a condition within an if clause, etc.) is satisfied, for example, by evaluating a logical expression based on the SCI monitoring result (in this case, the retransmission decision may or may not be stored in a variable);

[0139] - Determining the value of a termination decision variable (eg, a Boolean variable) indicating a retransmission decision, for example, by evaluating a logical expression based on the SCI monitoring result.

[0140] For example, terminating the HARQ process can be determined as a termination decision. For example, this termination decision can be called "Termination!". Furthermore, for example, not terminating the HARQ process can be determined as a termination decision. For example, this termination decision can be called "No termination!". The terms "Termination!" and "No termination!" are used herein for illustrative purposes only and are not limiting. For example, "TRUE" or "yes" can be used instead of "Termination!", and "FALSE" or "no" can be used instead of "No termination!".

[0141] According to another exemplary embodiment of the first exemplary aspect, the method further comprises:

[0142] -Monitoring the sidelink HARQ feedback from the receiver to the relay to obtain SL HARQ feedback monitoring results, and

[0143] - Optionally, a release decision on whether to release the relay device is determined according to the SL HARQ feedback monitoring result.

[0144] When a relay device relays data to a receiver using unicast SL HARQ, the transmitter can monitor the SL HARQ feedback from the receiver to the relay device, provided that the transmitter receives at least SCI according to the previous exemplary embodiment, and derive the physical SL feedback channel (PSFCH) resources used by the receiver to send SL HARQ feedback to the relay device. For example, this monitoring can be used to determine whether the receiver has become directly reachable to the transmitter and thus whether relaying is still required.

[0145] For example, determining a release decision may include one or more of the following:

[0146] - Determining whether a predefined condition for the release decision (e.g., a condition within an if clause, etc.) is satisfied, for example, by evaluating a logical expression based on the SL HARQ feedback monitoring result (in this case, the retransmission decision may or may not be stored in a variable);

[0147] - Determining the value of a release decision variable (eg, a Boolean variable) indicating a retransmission decision, for example, by evaluating a logical expression according to the SL HARQ feedback monitoring result.

[0148] For example, releasing the relay device can be determined as a releasing decision. For example, the releasing decision can be called "Releasing!". Furthermore, for example, not releasing the relay device can be determined as a releasing decision. For example, the releasing decision can be called "No releasing!". The terms "Releasing!" and "No releasing!" are used herein for illustrative purposes only and are not limiting. For example, "TRUE" or "yes" can be used instead of "Releasing!", and "FALSE" or "no" can be used instead of "No releasing!".

[0149] According to another exemplary embodiment of the first exemplary aspect, the method further comprises:

[0150] - monitoring the sidelink HARQ feedback from the receiver to the transmitter or to the relay to obtain SL HARQ feedback monitoring results, and

[0151] -Release the relay device based on the SL HARQ feedback monitoring results.

[0152] Based on monitoring the SL HARQ feedback from the receiver (which is sent by the receiver to the transmitter or relay device), the transmitter may specifically release the relay connection and / or the relay device when the receiver becomes directly and appropriately reachable to the transmitter.

[0153] According to another exemplary embodiment of the first exemplary aspect, even when the direct SL is currently suffering from RLF, the transmitter (e.g., Tx UE) can use the ID of the relay device (e.g., R-UE), or keep using the ID of the receiver (e.g., Rx UE), or flexibly alternate between them as the DSTID for sending data to the relay device and / or both the relay device and the receiver.

[0154] According to another exemplary embodiment of the first exemplary aspect, based on, for example, whether the relay is used for SL dual connectivity (for duplication or splitting of SL data from a transmitter to a receiver), for SL RLF recovery, or for power saving of the transmitter, whether the relay is visible or invisible to the receiver, the transmitter (e.g., Tx UE) can determine which ID of the relay device (e.g., R-UE) and the receiver (e.g., Rx UE) is used as the DST ID for SL transmission (e.g., in visible relay, the ID of the transmitter or relay device can be used by the relay device as the SRC ID to relay data to the receiver, while in invisible relay, the ID of the transmitter can be used by the relay device as the SRCID).

[0155] According to another exemplary embodiment of the first exemplary aspect, even when the direct SL is currently experiencing RLF, the transmitter (e.g., Tx UE) can maintain and use the SL radio bearer (RB) context of the direct SL between the transmitter and the receiver (e.g., Rx UE) in relay mode via a relay device (e.g., R-UE). This may mean that the relay device can retain all SL RB contexts of the direct SL mode received from the transmitter and, if necessary (e.g., for invisible relay), use them in this way or use them with a 1:1 mapping to relay corresponding data to the receiver. Current SL PDCP duplicate detection can be reused at the receiver in this way because the receiver can receive the same PDCP PDU from both the relay device and the transmitter on both the relay and direct connection.

[0156] According to another exemplary embodiment of the first exemplary aspect, the method further comprises:

[0157] - Execute a relay establishment procedure for establishing a relay device.

[0158] Specifically, a relay establishment procedure is performed prior to the transmission of at least one HARQ transmission. The relay establishment procedure specifically includes the transmission of a sidelink control message including identifier information indicating an identifier of a receiver and / or transmitter. Such a sidelink control message can specifically be received by a relay device. In this manner, the relay device can be informed of the identifiers of the transmitter and / or receiver.

[0159] The UE-to-UE relay setup procedure can include the configuration of the proposed enhanced multicast procedure. Thus, by using the receiver's ID as the multicast DSTID, the relay device can be aware of the multicast transmission. Furthermore, if the relay device needs to send a NACK back to the transmitter, it can also be aware of its dedicated PSFCH resources.

[0160] According to another exemplary embodiment of the first exemplary aspect, the method is performed by a mobile device and / or an IoT device, or is performed together with a mobile device and / or an IoT device. Specifically, the transmitter can be a mobile device and / or an IoT device.

[0161] According to an exemplary embodiment of the second exemplary aspect, determining the relay decision includes:

[0162] - If the receiver HARQ feedback monitoring result indicates discontinuous transmission (eg, HARQ DTX), determining to relay data of at least one HARQ transmission to the receiver.

[0163] For example, a receiver HARQ feedback monitoring result indicating discontinuous transmission may indicate that the receiver is unable to receive the HARQ transmission, and thus, for example, desires relaying via a relay device. Therefore, in this case, the relay decision may be determined as "Relay!".

[0164] According to another exemplary embodiment of the second exemplary aspect, determining the relay decision includes:

[0165] - If the receiver HARQ feedback monitoring result indicates a negative acknowledgement (eg, HARQ NACK), determining to relay data of at least one HARQ transmission to the receiver.

[0166] For example, a receiver HARQ feedback indicating a negative acknowledgement may indicate that the receiver has received the HARQ transmission, but unsuccessfully (e.g., only partially or with errors), and therefore, for example, relaying via a relay device is desired. Thus, in this case, the relay decision may be determined to be "Relay!"

[0167] According to another exemplary embodiment of the second exemplary aspect, the method further comprises:

[0168] - If at least one HARQ transmission is not successfully received, transmitting relay HARQ feedback indicating a negative acknowledgement (eg, HARQ NACK) to the transmitter.

[0169] In this way, the transmitter may be informed that a HARQ transmission was not successfully received, thereby anticipating transmission of a HARQ retransmission, enabling the relay device to successfully receive the retransmission and, if necessary, relay data from the HARQ retransmission to the receiver.

[0170] According to another exemplary embodiment of the second exemplary aspect, the method further comprises:

[0171] - Receiving at least one HARQ retransmission of a sidelink transport block from the transmitter.

[0172] Specifically, the method may further include: receiving at least one HARQ retransmission of the sidelink transport block from the transmitter after transmitting the relay HARQ feedback indicating a negative acknowledgement.

[0173] The HARQ retransmission may specifically include destination identifier information indicating a destination identifier of the relay device.

[0174] According to another exemplary embodiment of the second exemplary aspect, the method further comprises:

[0175] - Skipping transmission of relay HARQ feedback indicating a positive acknowledgement (eg, HARQ ACK) to the transmitter if at least one HARQ transmission has been successfully received.

[0176] In this way, a transmitter (e.g., a transmitter according to the first exemplary aspect) can infer from the discontinuous transmission from the relay device that the HARQ transmission has been successfully received, such that, for example, no retransmission is required, and the relay device will, for example, relay the data from the transmission to the receiver.

[0177] According to SL HARQ Opt-2, relay HARQ feedback may specifically be transmitted on a dedicated physical SL feedback channel (PSFCH), either as a multicast SL HARQ for at least one HARQ transmission, or as a unicast SL HARQ for at least one HARQ retransmission.

[0178] According to another exemplary embodiment of the second exemplary aspect, the method further comprises:

[0179] - Relaying data of at least one HARQ transmission or HARQ retransmission to the receiver based on the relay decision.

[0180] Specifically, if the retransmission decision is "Relay!", relaying of at least one HARQ transmission or HARQ retransmission data may be performed, whereas if the retransmission decision is "No relay!", relaying of at least one HARQ transmission or HARQ retransmission data may be skipped.

[0181] According to another exemplary embodiment of the second exemplary aspect, the method further comprises:

[0182] -Monitoring the sidelink HARQ feedback for the relay data from the receiver to obtain a sidelink HARQ feedback monitoring result.

[0183] In this way, the relay device can monitor whether the relay is successful.

[0184] Monitoring the sidelink HARQ feedback for the relay data from the receiver may specifically include monitoring the sidelink HARQ feedback for the relay data from the receiver.

[0185] According to another exemplary embodiment of the second exemplary aspect, a relay device (e.g., R-UE) may monitor SL HARQ feedback from a receiver (e.g., Rx UE) to a transmitter (e.g., Tx UE). In this way, the relay device may be able to determine whether the scheduled TB or the SL data in the scheduled TB needs to be relayed to the receiver.

[0186] According to another exemplary embodiment of the second exemplary aspect, relaying a TB from a relay device (e.g., R-UE) to a receiver (e.g., Rx UE) may use the same or different HARQ process as the original transmission from a transmitter (e.g., Tx UE).

[0187] Specifically, in the case where the relay TB uses a different HARQ process, the receiver (eg, Rx UE) may decode using, for example, the reception from the relay device (eg, R-UE).

[0188] More specifically, in another case, if the relayed TB uses the same HARQ process, the receiver (e.g., Rx UE) can, for example, decode using reception from both the relay device (e.g., R-UE) and the transmitter (e.g., Tx UE). In this case, the transmitter can, for example, start / pause transmission for a new TB upon receiving an indication from the relay device regarding whether the previous TB using the same HARQ process was acknowledged by the receiver.

[0189] According to a further exemplary embodiment of the second exemplary aspect, the at least one HARQ transmission of the sidelink transport block is the first HARQ transmission of the sidelink transport block, in particular the first HARQ transmission of more than one, e.g. consecutive, HARQ transmissions of the sidelink transport block.

[0190] According to another exemplary embodiment of the second exemplary aspect, the method is performed by a mobile device and / or an IoT device, or is performed together with a mobile device and / or an IoT device. Specifically, the relay device can be a mobile device and / or an IoT device.

[0191] The features and exemplary embodiments of the present disclosure described above may be equally applicable to different aspects according to the present disclosure.

[0192] It should be understood that the presentation of the disclosure in this section is by way of example only and is non-limiting.

[0193] Other features of the present disclosure will become apparent from the following detailed description considered in conjunction with the accompanying drawings. However, it should be understood that the drawings are designed for illustrative purposes only and are not intended as a definition of the limits of the present invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not drawn to scale and are intended merely to conceptually illustrate the structures and procedures described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0194] In the accompanying drawings, it is shown:

[0195] Figure 1 is a schematic block diagram of a system according to an exemplary aspect;

[0196] Figure 2 is a schematic block diagram of a system according to an exemplary aspect;

[0197] Figure 3 is a signaling diagram illustrating an example embodiment of the method according to the first exemplary aspect and further illustrating an example embodiment of the method according to the second exemplary aspect;

[0198] Figure 4 is a signaling diagram illustrating another exemplary embodiment of the method according to the first exemplary aspect and further illustrating another exemplary embodiment of the method according to the second exemplary aspect;

[0199] Figure 5 is a signaling diagram illustrating another exemplary embodiment of the method according to the first exemplary aspect and further illustrating another exemplary embodiment of the method according to the second exemplary aspect;

[0200] Figure 6 is a schematic block diagram of an apparatus configured to perform the method according to the first exemplary aspect; and

[0201] Figure 7 is a schematic block diagram of an apparatus configured to perform the method according to the second exemplary aspect. DETAILED DESCRIPTION

[0202] The following description is intended to enhance understanding of the present disclosure and should be understood as supplementary to and read together with the description provided in the above Summary section of this specification.

[0203] Figure 1 FIG1 is an example of a schematic high-level block diagram illustrating unicast SL transmission using HARQ Opt-2 between a transmitter 110 and a receiver 120 of the system 100. In this example, the transmitter 110 is a user equipment (Tx UE) and the receiver is a user equipment (Rx UE). The Tx UE and the Rx UE can each be a mobile device such as a cellular phone.

[0204] HARQ Opt-2 for unicast SL may include some or all of the following steps:

[0205] Step 151: The Tx UE transmits the first-stage sidelink control information (SCI) to the Rx UE on the physical SL control channel (PSCCH).

[0206] Step 152: The Tx UE transmits the second-stage SCI and TB HARQ to the Rx UE on the physical SL shared channel (PSSCH).

[0207] Step 153: The Tx UE expects feedback on the TB from the Rx UE. The feedback may be a positive acknowledgement (e.g., HARQ ACK), a negative acknowledgement (e.g., HARQ NACK), or discontinuous transmission (e.g., HARQ DTX) (if the Tx UE does not receive feedback within a specified time period).

[0208] Figure 2 2 is an example of a schematic high-level block diagram of a system according to exemplary aspects of the present disclosure. The system 200 includes a transmitter Tx UE 210 , a receiver Rx UE 230 , and a relay R-UE 220 .

[0209] Tx UE 210 is using SL-based UE-to-UE relay via relay device R-UE 220 to transmit SL data to Rx UE 230 because the direct SL between Tx UE 210 and Rx UE 230 is currently suffering from, for example, poor sidelink radio conditions or even SL RLF. It is assumed that a suitable R-UE 220 authorized to assist the communication between Tx UE 210 and Rx UE 230 has been discovered and selected.

[0210] The process of SL-based UE-to-UE relay from a transmitter (e.g., Tx UE 210) to a receiver (e.g., Rx UE 230) via a relay device (e.g., R-UE 220) may include some or all of the following steps of a HARQ scheme, such as based on hybrid multicast unicast SL HARQ Opt-2:

[0211] 1. The Tx UE may send at least the first HARQ transmission of the SL TB to both the R-UE and the Rx UE based on using, for example, enhanced multicast SL HARQ Opt-2, where the ID of the Rx UE is used as the DSTID to address the transmission, for example, with the following enhancements:

[0212] a. The Rx UE may behave the same as in the current SL HARQ Opt-2 (no enhancements are made to the Rx UE). Thus, when the Rx UE is able to successfully or unsuccessfully receive the SL TB indicated by the receive SCI, the Rx UE may send a HARQ ACK / NACK to the Tx UE, respectively (e.g., on the PSFCH mapped on the resources used to transmit the TB, as indicated in the receive SCI coupled with the IDs of the Tx UE and the Rx UE), e.g., as specified in conventional SL HARQ Opt-2. Otherwise, if the Rx UE fails to receive the transmit SCI from the Tx UE, the Tx UE expects HARQ DTX (e.g., no receiver HARQ feedback) from the Rx UE.

[0213] b. In the event that the R-UE successfully receives a SL TB, instead of sending a HARQ ACK to the Tx UE as in conventional SL HARQ Opt-2, the R-UE can be configured to monitor the Rx UE's HARQ ACK / NACK / DTX in (1.a.) and determine whether it is necessary to relay the SL data in the receive TB to the Rx UE or receive the TB. In this case, since the Tx UE expects HARQ DTX from the R-UE, it enables the R-UE to monitor the Rx UE's HARQ. Note that, for example, the R-UE can derive a dedicated PSFCH for the Rx UE and monitor HARQ feedback from the Rx UE based on the SCI received from the Tx UE and the IDs of both the Rx UE and the Tx UE, which are known to the R-UE during relay establishment.

[0214] i. Table 1 below provides the possible options and results for this determination step.

[0215] c. In case the R-UE does not successfully receive the SL TB, the R-UE may be configured to send a HARQ NACK to the Tx UE, as in conventional SL HARQ Opt-2.

[0216] 2. The Tx UE receives HARQ feedback for at least the first HARQ transmission of the SL TB from the R-UE and the Rx UE based on using multicast SL HARQ Opt-2 to expect HARQ ACK or HARQ NACK or HARQ DTX from the Rx UE and HARQ NACK or HARQ DTX (i.e., no HARQ ACK) from the R-UE, as described in (1.b.).

[0217] 3. The Tx UE sends at least one HARQ retransmission of the SL TB to the R-UE based on using unicast SL HARQ Opt-2, wherein at least in step 2, when the Tx UE receives a HARQ NACK from the R-UE and detects a HARQ DTX from the Rx UE, the ID of the R-UE is used as the DST ID to address the transmission.

[0218] By using multicast SL HARQ Opt-2 for at least the first HARQ transmission of the SL TB in step 1, this proposal enables the Tx UE to detect whether the Rx UE is directly reachable and how reachable it is compared to the R-UE based on monitoring HARQ feedback from both the Rx UE and the R-UE in step 2. This, in turn, can help the Tx UE determine whether the current UE-to-UE relay via the R-UE is still required without requiring any additional control overhead. That is, for example, upon receiving a HARQ ACK for the first HARQ transmission from the Rx UE in step 1, seamless return from UE-to-UE relay mode to direct SL mode is enabled for the Tx UE. Otherwise, the Tx UE maintains using UE-to-UE relay mode, and in step 3, if the Tx UE detects HARQ DTX from the Rx UE and a NACK from the R-UE, the Tx UE retransmits the SL TB only to the R-UE using unicast SL HARQ.

[0219] Table 1 below provides examples of UE behavior / operation according to the Tx UE according to possible monitoring HARQ feedback received from the Rx UE and R-UE in step 2 in the above HARQ scheme. The present disclosure is not limited to these examples.

[0220]

[0221] Table 1

[0222] the following Figure 3-Figure 5 In particular, the signaling diagrams corresponding to Case (1.1), Case (1.3) and Case (2.1) described in Table 1 are illustrated.

[0223] Figure 3 is a signaling diagram 300 illustrating an example embodiment of how SL data transmission between a transmitter Tx UE 310 and a receiver Rx UE 330 is performed using SL-based UE-to-UE relay via a relay device R-UE 320 . Figure 3 In particular, the example of case (1.1) in Table 1. For example, Tx UE 210 may be configured as Tx UE 310 , R-UE 220 may be configured as R-UE 320 , and / or Rx UE 230 may be configured as Rx UE 330 .

[0224] Figure 3 An exemplary embodiment of a method according to the first exemplary aspect is further shown, and an exemplary embodiment of a method according to the second exemplary aspect is further shown. Furthermore, a transmitter Tx UE 310 may be an exemplary embodiment of an apparatus according to the first exemplary aspect. Furthermore, a relay device R-UE 320 may be an exemplary embodiment of an apparatus according to the second exemplary aspect.

[0225] Figure 3 The process shown may include some or all of the following steps:

[0226] Step 350: Establish UE-to-UE relay for Tx UE 310 to transmit data to Rx UE 330 through SL. In this example, R-UE 320 is established as a relay device for the SL from Tx UE 310 to Rx UE 330.

[0227] In step 351, the Tx UE 310 initiates a HARQ process to transmit a TB.

[0228] Step 352: Tx UE 310 transmits the first HARQ transmission of the TB as a multicast using the ID of the Rx UE as the destination identifier. The transmission may reach the R-UE and / or the Rx UE. During or after this step, Tx UE 310 may further begin monitoring receiver HARQ feedback and relay HARQ feedback for the HARQ transmission.

[0229] Step 353a, the R-UE successfully receives the TB. Instead of sending HARQ ACK to the Tx UE, the receiver starts monitoring the HARQ feedback for the HARQ transmission from the Rx UE.

[0230] Step 353b: The Rx UE does not receive the HARQ transmission and therefore does not send receiver HARQ feedback.

[0231] Step 354a: Within a specified period of time after receiving the TB in step 353a, the R-UE 320, which is monitoring receiver HARQ feedback for the HARQ transmission, does not receive any receiver HARQ feedback from the Rx UE. Therefore, the receiver HARQ feedback monitoring result indicates HARQ DTX. Based on the obtained receiver HARQ feedback monitoring result, the R-UE determines a relay decision. In this example, the R-UE determines to relay ("Relay!") because the receiver HARQ feedback monitoring result indicates HARQ DTX.

[0232] Step 354b: Tx UE 310 is monitoring receiver HARQ feedback and relay HARQ feedback for the HARQ transmission. Due to steps 353a and 353b, the Tx UE has not received any receiver HARQ feedback from the Rx UE or any relay HARQ feedback from the R-UE within a specified period of time following the HARQ transmission in step 352. Therefore, in this example, both the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result indicate HARQ DTX. Based on the obtained receiver HARQ feedback monitoring result and the obtained relay HARQ feedback monitoring result, Tx UE 310 determines a retransmission decision. In this example, the Tx UE determines not to transmit a retransmission ("No retransmission!") because both the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result indicate HARQ DTX.

[0233] In step 355, based on the relay decision, the R-UE relays the TB. In this example, since the relay decision is "Relay!", the R-UE relays the TB to the Rx UE by transmitting the first HARQ transmission as a unicast using the Rx UE's ID as the destination identifier. The first HARQ transmission from the R-UE to the Rx UE may also reach the Tx UE, which may be monitoring sidelink HARQ feedback from the R-UE.

[0234] Step 356a, the Rx UE successfully receives the TB.

[0235] In step 356b, in this example, the first HARQ transmission from the R-UE to the Rx UE has also arrived at the Tx UE. Because the Tx UE is monitoring sidelink HARQ feedback from the R-UE, the Tx UE receives at least the SCI from the R-UE to the Rx UE. Based on the sidelink HARQ feedback monitoring results (in this example, the reception of the SCI), the Tx UE determines whether to terminate the HARQ process. In this example, the Tx UE determines to terminate ("Termination!") after receiving the SCI. Therefore, the Tx UE terminates the HARQ process.

[0236] Step 357: The Rx UE transmits a HARQ ACK to the R-UE, which can also reach the Tx UE. Therefore, based on the SCI received in step 356b, the Tx UE can monitor the sidelink HARQ feedback from the Rx UE to the R-UE. The monitoring results can be used to determine whether the Rx UE can reach the Tx UE.

[0237] In step 358, the R-UE receives the HARQ ACK from the R-UE and terminates the HARQ process.

[0238] Figure 3 The dashed lines in are the same transmissions from the transmitters, Tx UE 310 in step 352 and Rx UE 330 in step 357 .

[0239] Figure 3 The shown example covers an exemplary embodiment of a method according to the first exemplary aspect.Furthermore, the transmitter TxUE 310 may be an apparatus according to the first aspect or may be a part of an apparatus according to the first aspect.

[0240] The Tx UE 310 (which may be a mobile device such as a cellular phone) includes at least one processor and at least one memory including computer program code. The at least one memory and the computer program code are configured to, together with the at least one processor, cause the Tx UE to perform at least the following operations:

[0241] - in step 352, transmitting at least one HARQ transmission of the sidelink transport block, the at least one HARQ transmission including destination identifier information indicating a destination identifier of a receiver (eg, Rx UE 330),

[0242] - For example, from step 352 to step 354b, monitoring receiver HARQ feedback for at least one HARQ transmission from a receiver (e.g., Rx UE 330) to obtain a receiver HARQ feedback monitoring result indicating, for example, HARQ DTX as in step 354b,

[0243] - For example, from step 352 to step 354b, monitoring relay HARQ feedback for at least one HARQ transmission from a relay device (e.g., R-UE 320) to obtain a relay HARQ feedback monitoring result indicating, for example, HARQ DTX as in step 354b, and

[0244] - For example, in step 354b, a retransmission decision regarding whether to transmit at least one HARQ retransmission of the sidelink transport block is determined based on the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result, wherein in this example, the retransmission decision is, for example, "No retransmission!".

[0245] Figure 3 The shown example also covers exemplary embodiments of the method according to the second exemplary aspect.Furthermore, the relay device R-UE 320 may be an apparatus according to the second aspect or may be a part of an apparatus according to the second aspect.

[0246] The R-UE 320 (which may be a mobile device such as a cellular phone) includes at least one processor and at least one memory including computer program code. The at least one memory and the computer program code are configured to, together with the at least one processor, cause the R-UE to at least perform the following operations:

[0247] - in step 353a, receiving at least one HARQ transmission of a sidelink transport block from a transmitter (e.g., Tx UE 310), the HARQ transmission including destination identifier information indicating a destination identifier of a receiver (e.g., Rx UE 330), and

[0248] - at least in the case where the HARQ transmission has been successfully received (e.g., as was the case in step 353a),

[0249] - For example, from steps 353a to 354a, monitoring receiver HARQ feedback for HARQ transmission from a receiver (eg, Rx UE 330) to obtain a receiver HARQ feedback monitoring result indicating, for example, HARQ DTX as in step 354a, and

[0250] - For example, in step 354a, a relay decision is determined based on the receiver HARQ feedback monitoring result as to whether to relay at least the HARQ transmitted data to the receiver (eg, Rx UE 330), in this example, the relay decision is e.g.

[0251] “Relay!”.

[0252] Figure 4 is a signaling diagram 400 illustrating another example embodiment of how SL data transmission between a transmitter Tx UE 410 and a receiver Rx UE 430 is performed using SL-based UE-to-UE relay via a relay Rx UE 430 . Figure 4 In particular, the example of case (1.3) in Table 1. For example, Tx UE 210 may be configured as Tx UE 410 , R-UE 220 may be configured as R-UE 420 , and / or Rx UE 230 may be configured as Rx UE 430 .

[0253] Figure 4 The process shown may include some or all of the following steps:

[0254] Step 450: Establish a UE-to-UE relay for the Tx UE 410 to transmit data to the Rx UE 420 through the SL (this step corresponds to step 350).

[0255] Step 451 , which corresponds to step 351 .

[0256] Step 452 : This step corresponds to step 352 .

[0257] Step 453a, this step corresponds to step 353a.

[0258] Step 453b, in this example, the Rx UE successfully receives the TB.

[0259] Step 454: When the Rx UE successfully receives the TB in step 453b, the Rx UE sends a HARQ ACK as receiver HARQ feedback.

[0260] Step 455a: Tx UE 410 is monitoring receiver HARQ feedback and relay HARQ feedback for the HARQ transmission. According to steps 453a and 454, Tx UE receives a HARQ ACK as receiver HARQ feedback from Rx UE 430, and does not receive any relay HARQ feedback from R-UE 420 within a specified period of time following the HARQ transmission in step 452. Therefore, in this example, the receiver HARQ feedback monitoring result indicates HARQ ACK, while the relay HARQ feedback monitoring result indicates HARQ DTX. Based on the obtained receiver HARQ feedback monitoring result and the obtained relay HARQ feedback monitoring result, Tx UE 410 determines a retransmission decision. In this example, Tx UE determines not to transmit a retransmission ("No retransmission!") because the receiver HARQ feedback monitoring result indicates HARQ ACK.

[0261] Step 455b: The R-UE 420, which is monitoring receiver HARQ feedback for the HARQ transmission, receives the HARQ ACK feedback sent by the Rx UE, such that the receiver HARQ feedback monitoring result indicates HARQ ACK. Based on the obtained receiver HARQ feedback monitoring result, the R-UE determines a relay decision. In this example, the R-UE determines not to relay ("No relay!") because the receiver HARQ feedback monitoring result indicates HARQ ACK.

[0262] In step 456a, the Tx UE determines a termination decision based on the receiver HARQ feedback monitoring result. In this example, the Tx UE determines to terminate the HARQ process because the receiver HARQ feedback monitoring result indicates HARQ ACK.

[0263] In step 456b, the R-UE terminates the HARQ process according to the relay decision. In this example, since the relay decision is "No relay!", the R-UE terminates the HARQ process.

[0264] In step 457, the Tx UE 410 determines a release decision based on the receiver HARQ feedback monitoring result. In this example, the Tx UE determines to release the relay device ("Releasing!") because the receiver HARQ feedback monitoring result indicates HARQ ACK, which indicates that the HARQ ACK can be returned to direct SL.

[0265] In step 458, the Tx UE releases the relay device R-UE according to the release decision. In this example, the Tx UE releases the R-UE because the release decision is "Releasing!".

[0266] Figure 4 The dashed line in is the same transmission from the transmitter Tx UE 310 in step 352 .

[0267] Figure 4 The shown example covers an exemplary embodiment of a method according to the first exemplary aspect.Furthermore, the transmitter TxUE 410 may be an apparatus according to the first aspect or may be a part of an apparatus according to the first aspect.

[0268] The Tx UE 410 (which may be a mobile device such as a cellular phone) includes at least one processor and at least one memory including computer program code. The at least one memory and the computer program code are configured to, together with the at least one processor, cause the Tx UE to perform at least the following operations:

[0269] - in step 452, transmitting at least one HARQ transmission of the sidelink transport block, the at least one HARQ transmission including destination identifier information indicating a destination identifier of a receiver (eg, Rx UE 430),

[0270] - For example, from step 452 to step 455a, monitoring the data from the receiver (eg, Rx UE

[0271] 430) to obtain a receiver HARQ feedback monitoring result indicating, for example, a HARQ ACK as in step 455a,

[0272] - For example, from step 452 to step 455a, monitoring the data from the relay device (eg, R-UE

[0273] 420) for at least one HARQ transmission to obtain, for example, a relay HARQ feedback monitoring result indicating HARQ DTX as in step 455b, and

[0274] - For example, in step 455a, a retransmission decision regarding whether to transmit at least one HARQ retransmission of the sidelink transport block is determined based on the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result. In this example, the retransmission decision is, for example, "No retransmission!".

[0275] Figure 4 The shown example also covers exemplary embodiments of the method according to the second exemplary aspect.Furthermore, the relay device R-UE 420 may be an apparatus according to the second aspect or may be a part of an apparatus according to the second aspect.

[0276] The R-UE 420 (which may be a mobile device such as a cellular phone) includes at least one processor and at least one memory including computer program code. The at least one memory and the computer program code are configured to, together with the at least one processor, cause the R-UE to at least perform the following operations:

[0277] - in step 453a, receiving at least one HARQ transmission of a sidelink transport block from a transmitter (e.g., Tx UE 410), the HARQ transmission including destination identifier information indicating a destination identifier of a receiver (e.g., Rx UE 430), and

[0278] - at least in the case where the HARQ transmission has been successfully received (e.g., as in step 453a),

[0279] - For example, from steps 453a to 455b, monitoring receiver HARQ feedback for the HARQ transmission from the receiver (eg, Rx UE 430) to obtain a receiver HARQ feedback monitoring result indicating, for example, a HARQ ACK as in step 455b, and

[0280] - For example, in step 455b, a relay decision is determined based on the receiver HARQ feedback monitoring result as to whether the data of at least one HARQ transmission needs to be relayed to the receiver (eg, Rx UE 430), in this example, the relay decision is, for example, "No relay!".

[0281] Figure 5 is a signaling diagram 500 illustrating another example embodiment of how SL data transmission between a transmitter Tx UE 510 and a receiver Rx UE 520 is performed using SL-based UE-to-UE relay via a relay Rx UE 530 . Figure 5In particular, the example of case (2.1) in Table 1. For example, Tx UE 210 may be configured as Tx UE 510 , R-UE 220 may be configured as R-UE 520 , and / or Rx UE 230 may be configured as Rx UE 530 .

[0282] Figure 5 The process shown may include some or all of the following steps:

[0283] Step 550: Establish a UE-to-UE relay for the Tx UE 510 to transmit data to the Rx UE 530 through the SL (this step corresponds to step 350).

[0284] Step 551 , which corresponds to step 351 .

[0285] Step 552: This step corresponds to step 352.

[0286] Step 553a: R-UE 520 receives the first HARQ transmission sent by Tx UE 510 in step 552, but unsuccessfully (eg, only partially or with errors). R-UE 520 may or may not start monitoring receiver HARQ feedback for the HARQ transmission from the Rx UE.

[0287] Step 553b: The Rx UE does not receive the first HARQ transmission and therefore does not send receiver HARQ feedback.

[0288] Step 554: Since the HARQ transmission was not successfully received, the R-UE 520 transmits a relay HARQ feedback indicating a negative acknowledgement (eg, HARQ NACK) to the transmitter Tx UE 510.

[0289] Step 555: Tx UE 510 is monitoring receiver HARQ feedback and relay HARQ feedback for the HARQ transmission. According to steps 553a and 553b, Tx UE receives a HARQ NACK as relay HARQ feedback from R-UE 520, and does not receive any receiver HARQ feedback from Rx UE 530 within a specified period of time following the HARQ transmission in step 552. Therefore, in this example, the receiver HARQ feedback monitoring result indicates HARQ DTX, while the relay HARQ feedback monitoring result indicates HARQ NACK. Based on the acquired receiver HARQ feedback monitoring result and the acquired relay HARQ feedback monitoring result, Tx UE 510 determines a retransmission decision. In this example, the Tx UE determines to transmit a retransmission ("Retransmission!") because the receiver HARQ feedback monitoring result indicates HARQ DTX (thus relay is required) and because the relay HARQ feedback monitoring result indicates HARQ NACK (i.e., the R-UE 520 needs to retransmit to perform relay).

[0290] Step 556: Tx transmits the second HARQ transmission of the TB (ie, a HARQ retransmission), but this time it is unicast using the ID of the R-UE 520 as the destination identifier.

[0291] Step 557: The R-UE 520 successfully receives the second HARQ transmission (ie, HARQ retransmission) and thus receives the TB.

[0292] In step 558, the R-UE sends a HARQ ACK to the Tx UE to confirm the successful reception of the HARQ retransmission.

[0293] Step 559: The Tx UE receives the HARQ ACK from the R-UE and, based on this, determines to terminate the HARQ process ("Termination!"). Therefore, the Tx UE then terminates the HARQ process.

[0294] Step 560: When the R-UE receives a TB from the Tx UE on a HARQ retransmission (the second HARQ transmission in this example), the R-UE determines to relay the TB to the Rx UE ("Relay!"). Thus, the R-UE flexibly relays the received TB itself or the data within the TB to the Rx UE.

[0295] Figure 5 The dashed line in is the same transmission from the transmitter Tx UE 310 in step 352 .

[0296] Figure 5The shown example covers an exemplary embodiment of the method according to the first exemplary aspect.Furthermore, the transmitter TxUE 510 may be an apparatus according to the first aspect or may be a part of an apparatus according to the first aspect.

[0297] The Tx UE 510 (which may be a mobile device such as a cellular phone) includes at least one processor and at least one memory including computer program code. The at least one memory and the computer program code are configured to, together with the at least one processor, cause the Tx UE to perform at least the following operations:

[0298] - in step 552, transmitting at least one HARQ transmission of the sidelink transport block, the at least one HARQ transmission including destination identifier information indicating a destination identifier of a receiver (eg, Rx UE 530),

[0299] - For example, from step 552 to step 555, monitoring receiver HARQ feedback for at least one HARQ transmission from a receiver (e.g., Rx UE 530) to obtain a receiver HARQ feedback monitoring result indicating, for example, HARQ DTX as in step 355,

[0300] - For example, from step 552 to step 555, monitoring the data from the relay device (eg, R-UE

[0301] 520) for at least one HARQ transmission to obtain, for example, a relay HARQ feedback monitoring result indicating a HARQ NACK as in step 555, and

[0302] - For example, in step 555, a retransmission decision is determined based on the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result as to whether at least one HARQ retransmission of the sidelink transport block needs to be transmitted, in this example, the retransmission decision is e.g.

[0303] "Retransmission!"

[0304] - Therefore, the Tx UE 510 transmits a HARQ retransmission in step 556 .

[0305] Figure 5 The shown example also covers exemplary embodiments of the method according to the second exemplary aspect.Furthermore, the relay device R-UE 520 may be an apparatus according to the second aspect or may be a part of an apparatus according to the second aspect.

[0306] The R-UE 520 (which may be a mobile device such as a cellular phone) includes at least one processor and at least one memory including computer program code. The at least one memory and the computer program code are configured to, together with the at least one processor, cause the R-UE to at least perform the following operations:

[0307] - in step 553a, receiving at least one HARQ transmission of a sidelink transport block from a transmitter (e.g., Tx UE 510), the HARQ transmission including destination identifier information indicating a destination identifier of a receiver (e.g., Rx UE 530),

[0308] - in step 554, if at least one HARQ transmission is not successfully received, a relay HARQ feedback indicating a negative acknowledgement (e.g., HARQ NACK) is transmitted to the transmitter (e.g., Tx UE 510), which is the case in step 553a in this example,

[0309] - After the transmission of the relay HARQ feedback message indicating negative acknowledgement information in step 554, at least one HARQ retransmission of the sidelink transport block is received from the transmitter (e.g., Tx UE 520) in step 557, Figure 5 is referred to as the "second HARQ transmission", and

[0310] - In step 560, at least one HARQ retransmitted data is relayed to a receiver (eg, Rx UE 530).

[0311] In another example, the Tx UE may use enhanced SL HARQ Opt-2 of options (1.1) and (1.2) in Table 1 to transmit more than one consecutive HARQ (re)transmission, including the first HARQ transmission of a TB, to achieve reassurance (i.e., it is expected that the R-UE will successfully receive the TB). That is, for all these HARQ (re)transmissions, the Tx UE detects / receives DTX from the R-UE and NACK / DTX from the Rx UE before terminating the HARQ process.

[0312] In another example, the Tx UE may monitor at least the SCI sent by the R-UE to the Rx UE, which the R-UE uses to schedule data transmission to the Rx, to ensure that the R-UE is receiving data from the Tx UE and relaying data to the Rx. This monitoring is also used to enable the Tx UE to monitor HARQ feedback from the Rx UE to the R-UE, as described in the next example. This monitoring can be used by the Tx UE to determine whether to terminate the HARQ process for options (1.1) and (1.2) in Table 1.

[0313] In another example, the Tx UE can monitor the SL HARQ feedback from the Rx UE to the R-UE when the R-UE relays data to the Rx UE using unicast SL HARQ, provided that the Tx UE receives at least SCI in the previous example, and derive the PSFCH resources used by the Rx UE to send SL HARQ to the R-UE. This monitoring is used to determine whether the Rx UE becomes directly reachable to the Tx UE and therefore whether relaying is still required.

[0314] Note that this monitoring can also be applied to R-UE, as mentioned above in conjunction with Figure 2 However, the purpose is different: the R-UE monitors the SL HARQ feedback from the Rx UE to the Tx UE in order to decide whether the SL data in the scheduled TB or the scheduled TB needs to be relayed to the Rx UE.

[0315] In another example, based on the SL HARQ feedback from the Rx UE sent by the Rx UE to the Tx UE or R-UE, the Tx UE may release the relay connection and the R-UE when the Rx UE becomes directly and appropriately reachable to the Tx UE.

[0316] In another example, the Tx UE may use the R-UE's ID, or keep using the Rx UE's ID, or flexibly alternate between them as the DST ID for sending data to the R-UE and / or both the R-UE and the Rx UE, even when the direct SL currently suffers from RLF.

[0317] In another example, based on, for example, whether the relay is used for SL dual connectivity (for duplication or splitting of SL data from the Tx UE to the Rx UE), for SL RLF recovery, or for power saving of the Tx UE, whether the relay is visible or invisible to the Rx UE, the Tx UE can determine which ID of the R-UE and the Rx UE is used as the DST ID for SL transmission (in visible relay, the ID of the Tx UE or the R-UE can be used by the R-UE as the SRC ID to relay data to the Rx UE, while in invisible relay, the ID of the Tx UE is used by the R-UE as the SRC ID).

[0318] In another example, even when the direct SL is currently experiencing RLF, the Tx UE can maintain and use the SL radio bearer (RB) context of the direct SL between the Tx UE and the Rx UE via the R-UE in relay mode. This can mean that the R-UE can retain all SL RB contexts of the direct SL mode received from the Tx UE and, if necessary (e.g., for invisible relay), can use them in this way or use them with a 1:1 mapping to relay the corresponding data to the Rx UE. Current SL PDCP duplicate detection can be reused at the Rx UE in this way because the Rx UE can receive the same PDCP PDU from both the R-UE and the Tx UE on both relay and direct connections.

[0319] In another example, relaying a TB from the R-UE to the Rx UE may use the same or a different HARQ process as the original transmission from the Tx UE.

[0320] - In case the relay TB uses a different HARQ process, the Rx UE can decode using only the reception from the R-UE.

[0321] In another case, if the relay TB uses the same HARQ process, the Rx UE can use the reception from both the R-UE and the Tx UE for decoding. In this case, the Tx UE can, for example, start / pause its transmission for the new TB upon receiving an indication from the R-UE as to whether the previous TB using the same HARQ process was acknowledged by the Rx UE.

[0322] In another example, the UE-to-UE relay setup procedure can include the configuration of the proposed enhanced multicast procedure. Thus, for example, by using the ID of the Rx UE as the DST ID for the multicast, the R-UE can be aware of the multicast transmission. In addition, if the R-UE needs to send a NACK back to the Tx UE, the R-UE can also be aware of its dedicated PSFCH resources.

[0323] Figure 6 is a schematic block diagram of an apparatus 600 according to an exemplary aspect of the present invention, which may, for example, represent Figure 2 Tx UE 210.

[0324] The apparatus 600 comprises a processor 610 , a working memory 620 , a program memory 630 , a data memory 640 , a communication interface(s) 650 , an optional user interface 660 and an optional sensor(s) 670 .

[0325] The apparatus 600 may, for example, be configured to execute and / or control the method according to the first exemplary aspect, or include corresponding components (at least one of 610 to 670) for executing and / or controlling the method according to the first exemplary aspect. The apparatus 600 may also constitute an apparatus comprising at least one processor (610) and at least one memory (620) including computer program code, the at least one memory and the computer program code being configured to, together with the at least one processor, cause the apparatus (e.g., apparatus 600) to at least execute and / or control the method according to the first exemplary aspect.

[0326] The processor 610 may, for example, include a transmission initiator 611 as a functional and / or structural unit. The transmission initiator 611 may, for example, be configured to initiate the transmission of a message, such as a HARQ transmission, a HARQ retransmission, or a HARQ feedback transmission, to name a few non-limiting examples. The transmission initiator 611 may, for example, be configured to initiate the transmission of a message as a unicast or multicast.

[0327] The processor 610 may, for example, include as a functional and / or structural unit a monitoring initiator 612. The monitoring initiator 612 may, for example, be configured to start monitoring messages, e.g., for HARQ transmissions, for HARQ feedback (such as receiver HARQ feedback or relay HARQ feedback), or to start monitoring the absence of messages, e.g., for HARQ transmissions or for HARQ feedback, e.g., within a specified time period.

[0328] The processor 610 may, for example, include a determining unit 613 as a functional and / or structural unit. For example, the determining unit 613 may be configured to determine a decision, such as a retransmission decision, a relay decision, a termination decision, or a release decision, based on information such as HARQ feedback monitoring results (such as receiver HARQ feedback monitoring results and / or relay HARQ feedback monitoring results, to name a few non-limiting examples).

[0329] The processor 610 may include, for example, as a functional and / or structural unit, a termination executor 614. The termination executor 614 may, for example, be configured to perform termination of a process (eg, a HARQ process).

[0330] The processor 610 may include, for example, a release executor 615 as a functional and / or structural unit. The release executor 615 may, for example, be configured to execute the release of the relay connection or device.

[0331] The processor 610 may include, for example, a relay establishment executor 616 as a functional and / or structural unit. The relay establishment executor 616 may, for example, be configured to execute a relay establishment procedure for establishing a relay device.

[0332] Processor 610 may, for example, further control memories 620 to 640 , communication interface(s) 650 , optional user interface 660 , and optional sensor(s) 670 .

[0333] The processor 610 may, for example, execute computer program code stored in a program memory 630 , which may, for example, represent a computer-readable storage medium comprising program code which, when executed by the processor 610 , causes the processor 610 to perform the method according to the first exemplary aspect.

[0334] Processor 610 (and any other processors mentioned in this specification) can be any suitable type of processor. Processor 610 can include, but is not limited to, one or more microprocessors, one or more processors with accompanying one or more digital signal processors, one or more processors without accompanying (multiple) digital signal processors, one or more special-purpose computer chips, one or more field programmable gate arrays (FPGAs), one or more controllers, one or more application-specific integrated circuits (ASICs), or one or more computers. The relevant structure / hardware has been programmed to perform the functions described above. Processor 610 can be, for example, an application processor running an operating system.

[0335] Program memory 630 may also be included in processor 610. This memory may, for example, be fixedly connected to processor 610, or may be at least partially removable from processor 610, for example in the form of a memory card or stick. Program memory 630 may, for example, be a non-volatile memory. For example, it may be any one of FLASH memory (or a portion thereof), ROM, PROM, EPROM, and EEPROM memory (or a portion thereof), or a hard disk (or a portion thereof), to name a few examples. Program memory 630 may also include an operating system for processor 610. Program memory 630 may also include firmware for device 600.

[0336] The apparatus 600 includes a working memory 620, for example in the form of a volatile memory. For example, it can be a random access memory (RAM) or a dynamic RAM (DRAM), to name a few non-limiting examples. It can be used, for example, by the processor 610 when executing an operating system and / or computer programs.

[0337] The data memory 640 may be, for example, a non-volatile memory. For example, it may be any one of a FLASH memory (or a portion thereof), a ROM, a PROM, an EPROM, and an EEPROM memory (or a portion thereof), or a hard disk (or a portion thereof), to name a few examples. The data memory 640 may, for example, store measurement configuration information, handover configuration information, RRC configuration, CPA configuration information, or a combination thereof, to name a few non-limiting examples.

[0338] Communication interface(s) 650 enable the apparatus 600 to communicate with other entities, such as Figure 2 The communication interface(s) 650 may, for example, include a wireless interface (e.g., a cellular radio communication interface and / or a WLAN interface) and / or a wired interface (e.g., an IP-based interface) to communicate with entities, for example, via the Internet. The communication interface(s) may enable the apparatus 600 to communicate with Figure 2 Communicates with other entities not shown.

[0339] The user interface 660 is optional and may include a display for displaying information to a user and / or an input device (eg, a keyboard, keypad, touchpad, mouse, etc.) for receiving information from a user.

[0340] Sensor(s) 670 are optional and may include, for example, an air pressure sensor for collecting pressure information.

[0341] Some or all components of the apparatus 600 may be connected, for example, via a bus. Some or all components of the apparatus 600 may be combined into one or more modules, for example.

[0342] Figure 7 is a schematic block diagram of an apparatus 700 according to an exemplary aspect of the present invention, which may, for example, represent Figure 2 R-UE 220 in.

[0343] The apparatus 700 comprises a processor 710 , a working memory 720 , a program memory 730 , a data memory 740 , a communication interface(s) 750 , an optional user interface 760 and an optional sensor(s) 770 .

[0344] The apparatus 700 may, for example, be configured to execute and / or control the method according to the second exemplary aspect, or include corresponding components (at least one of 710 to 770) for executing and / or controlling the method according to the second exemplary aspect. The apparatus 700 may also constitute an apparatus comprising at least one processor (710) and at least one memory (720) including computer program code, the at least one memory and the computer program code being configured to, together with the at least one processor, cause the apparatus (e.g., apparatus 700) to at least execute and / or control the method according to the second exemplary aspect.

[0345] The processor 710 may, for example, include as a functional and / or structural unit a reception controller 711. The reception controller 711 may, for example, be configured to control reception of messages, such as reception of HARQ transmissions, HARQ retransmissions, or HARQ feedback, to name a few non-limiting examples.

[0346] The processor 710 may, for example, include a transmission initiator 712 as a functional and / or structural unit. The transmission initiator 712 may, for example, be configured to initiate the transmission of a message, such as a HARQ transmission, a HARQ retransmission, or a HARQ feedback transmission, to name a few non-limiting examples. The transmission initiator 712 may, for example, be configured to initiate the transmission of a message as a unicast or multicast.

[0347] The processor 710 may, for example, include as a functional and / or structural unit a monitoring initiator 713. The monitoring initiator 713 may, for example, be configured to start monitoring messages, e.g., for HARQ transmissions, for HARQ feedback (such as receiver HARQ feedback or relay HARQ feedback), or to start monitoring the absence of messages, e.g., for HARQ transmissions or for HARQ feedback, e.g., within a specified time period.

[0348] The processor 710 may, for example, include a determining unit 714 as a functional and / or structural unit. For example, the determining unit 714 may be configured to determine a decision, such as a retransmission decision, a relay decision, a termination decision, or a release decision, based on information such as HARQ feedback monitoring results (such as receiver HARQ feedback monitoring results and / or relay HARQ feedback monitoring results, to name a few non-limiting examples).

[0349] The processor 710 may include, for example, a termination executor 715 as a functional and / or structural unit. The termination executor 715 may, for example, be configured to perform termination of a process (eg, a HARQ process).

[0350] Processor 710 may, for example, further control memories 720 to 740 , communication interface(s) 750 , optional user interface 760 , and optional sensor(s) 770 .

[0351] The processor 710 may, for example, execute computer program code stored in a program memory 730 , which may, for example, represent a computer-readable storage medium comprising program code which, when executed by the processor 710 , causes the processor 710 to perform the method according to the second exemplary aspect.

[0352] Processor 710 (and any other processors mentioned in this specification) can be any suitable type of processor. Processor 710 can include, but is not limited to, one or more microprocessors, one or more processors with accompanying one or more digital signal processors, one or more processors without accompanying (multiple) digital signal processors, one or more special-purpose computer chips, one or more field programmable gate arrays (FPGAs), one or more controllers, one or more application-specific integrated circuits (ASICs), or one or more computers. The relevant structure / hardware has been programmed to perform the functions described above. Processor 710 can be, for example, an application processor running an operating system.

[0353] A program memory 730 may also be included in the processor 710. This memory may, for example, be fixedly connected to the processor 710, or may be at least partially removable from the processor 710, for example in the form of a memory card or stick. The program memory 730 may, for example, be a non-volatile memory. For example, it may be any one of a FLASH memory (or a portion thereof), a ROM, a PROM, an EPROM, and an EEPROM memory (or a portion thereof), or a hard disk (or a portion thereof), to name a few examples. The program memory 730 may also include an operating system for the processor 710. The program memory 730 may also include firmware for the device 700.

[0354] The apparatus 700 includes a working memory 720, for example in the form of a volatile memory. For example, it can be a random access memory (RAM) or a dynamic RAM (DRAM), to name a few non-limiting examples. It can be used, for example, by the processor 710 when executing an operating system and / or computer programs.

[0355] The data memory 740 may be, for example, a non-volatile memory. For example, it may be any one of a FLASH memory (or a portion thereof), a ROM, a PROM, an EPROM, and an EEPROM memory (or a portion thereof), or a hard disk (or a portion thereof), to name a few examples. The data memory 640 may, for example, store measurement configuration information, handover configuration information, RRC configuration, CPA configuration information, or a combination thereof, to name a few non-limiting examples.

[0356] Communication interface(s) 750 enable the apparatus 700 to communicate with other entities, such as Figure 2 The communication interface(s) 750 may, for example, include a wireless interface (e.g., a cellular radio communication interface and / or a WLAN interface) and / or a wired interface (e.g., an IP-based interface) to communicate with an entity, for example, via the Internet. The communication interface(s) may enable the apparatus 700 to communicate with Figure 2 Communicates with other entities not shown.

[0357] The user interface 760 is optional and may include a display for displaying information to a user and / or an input device (eg, a keyboard, keypad, touchpad, mouse, etc.) for receiving information from a user.

[0358] Some or all components of the apparatus 700 may be connected, for example, via a bus. Some or all components of the apparatus 700 may be combined into one or more modules, for example.

[0359] The following embodiments are also considered to be disclosed:

[0360] Example A1:

[0361] An apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processor, cause the apparatus to at least perform:

[0362] - transmitting at least one HARQ transmission of a sidelink transport block, the at least one HARQ transmission comprising destination identifier information indicating a destination identifier of a receiver,

[0363] - monitoring receiver HARQ feedback for the at least one HARQ transmission from the receiver to obtain a receiver HARQ feedback monitoring result,

[0364] - monitoring relay HARQ feedback for the at least one HARQ transmission from the relay device to obtain a relay HARQ feedback monitoring result, and

[0365] - determining a retransmission decision regarding whether to transmit at least one HARQ retransmission of the sidelink transport block based on the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result.

[0366] Example A2:

[0367] The apparatus of embodiment A1, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0368] - transmitting the at least one HARQ retransmission according to the retransmission decision.

[0369] Example A3:

[0370] The device of embodiment A1 or A2, wherein:

[0371] - The HARQ retransmission includes destination identifier information indicating a destination identifier of the relay device.

[0372] Example A4:

[0373] The device of any one of Embodiments A1 to A3, wherein:

[0374] - Determining the retransmission decision comprises:

[0375] - determining to retransmit the at least one HARQ retransmission at least if the receiver HARQ feedback monitoring result indicates discontinuous transmission (e.g., HARQ DTX) and the relay HARQ feedback monitoring result indicates negative acknowledgement (e.g., HARQ NACK).

[0376] Example A5:

[0377] The device of any one of Embodiments A1 to A4, wherein:

[0378] - Transmitting the at least one HARQ transmission comprises:

[0379] - transmitting the at least one HARQ transmission as a multicast sidelink HARQ transmission.

[0380] Example A6:

[0381] The device of any one of Embodiments A1 to A5, wherein:

[0382] - Transmitting the at least one HARQ retransmission comprises:

[0383] - transmitting the at least one HARQ retransmission as a unicast sidelink HARQ (re)transmission.

[0384] Example A7:

[0385] The device of any one of Embodiments A1 to A6, wherein:

[0386] - Determining the retransmission decision comprises:

[0387] - in a case where the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate a negative acknowledgement (e.g., HARQ NACK),

[0388] A determination is made to transmit the at least one HARQ retransmission.

[0389] Example A8:

[0390] The device of any one of embodiments A1 to A7, wherein:

[0391] - Determining the retransmission decision comprises:

[0392] - in a case where the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate discontinuous transmission (e.g., HARQ DTX),

[0393] Determining not to transmit the at least one HARQ retransmission.

[0394] Example A9:

[0395] The apparatus of any one of embodiments A1 to A8, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0396] - In a case where the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate discontinuous transmission (eg, HARQ DTX), terminating the HARQ process.

[0397] Example A10:

[0398] The device of any one of embodiments A1 to A9, wherein

[0399] - Determining the retransmission decision comprises:

[0400] - if the receiver HARQ feedback monitoring result indicates a negative acknowledgement (eg, HARQ NACK) and the relay HARQ feedback monitoring result indicates discontinuous transmission (eg, HARQ DTX), determining not to transmit the at least one HARQ retransmission.

[0401] Example A11:

[0402] The apparatus of any one of embodiments A1 to A10, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0403] - If the receiver HARQ feedback monitoring result indicates negative acknowledgement (eg, HARQ NACK) and the relay HARQ feedback monitoring result indicates discontinuous transmission (eg, HARQ DTX), terminating the HARQ process.

[0404] Example A12:

[0405] The device of any one of embodiments A1 to A11, wherein

[0406] - Determining the retransmission decision comprises:

[0407] - If the receiver HARQ feedback monitoring result indicates a positive acknowledgement (eg, HARQ ACK), determining not to transmit the at least one HARQ retransmission.

[0408] Example A13:

[0409] The apparatus of any one of embodiments A1 to A12, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0410] - If the receiver HARQ feedback monitoring result indicates a positive acknowledgement (eg, HARQ ACK), terminating the HARQ process.

[0411] Example A14:

[0412] The apparatus of any one of embodiments A8 to A13, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0413] - releasing the relay device.

[0414] Example A15:

[0415] The apparatus of any one of embodiments A1 to A14, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0416] - transmitting more than one consecutive HARQ transmission of said sidelink transport block,

[0417] - monitoring a corresponding receiver HARQ feedback for a corresponding HARQ transmission from the receiver to obtain a corresponding receiver HARQ feedback monitoring result, and

[0418] - monitoring corresponding relay HARQ feedback for corresponding HARQ transmission from the relay device to obtain corresponding relay HARQ feedback monitoring results,

[0419] - determining a respective retransmission decision regarding whether to transmit at least one respective HARQ retransmission of the sidelink transport block based on the respective receiver HARQ feedback monitoring result and the respective relay HARQ feedback monitoring result.

[0420] Example A16:

[0421] The apparatus of any one of embodiments A1 to A15, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0422] - monitoring a message including sidelink control information (SCI) from the relay device to the receiver to obtain an SCI monitoring result, and

[0423] - Optionally, determining a termination decision on whether to terminate the HARQ process according to the SCI monitoring result.

[0424] Example A17:

[0425] The apparatus of any one of embodiments A1 to A16, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0426] - monitoring the sidelink HARQ feedback from the receiver to the relay to obtain SL HARQ feedback monitoring results, and

[0427] - Optionally, determining a release decision on whether to release the relay according to the SL HARQ feedback monitoring result.

[0428] Example A18:

[0429] The apparatus of any one of embodiments A1 to A17, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0430] - monitoring the sidelink HARQ feedback from the receiver to the transmitter or to the relay device to obtain SLHARQ feedback monitoring results, and

[0431] -Release the relay device according to the SL HARQ feedback monitoring result.

[0432] Example A19:

[0433] The apparatus of any one of embodiments A1 to A18, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0434] - performing a relay establishment procedure for establishing the relay device.

[0435] Example A20:

[0436] The apparatus according to any one of embodiments A1 to A19, wherein the apparatus is a mobile device and / or an Internet of Things (IoT) device, or is a part of a mobile device and / or an Internet of Things (IoT) device.

[0437] Example A21:

[0438] The apparatus of any one of embodiments A1 to A20, wherein the at least one HARQ transmission of the sidelink transport block is a first HARQ transmission of the sidelink transport block.

[0439] Example A22:

[0440] The apparatus of embodiment A15, wherein the more than one consecutive HARQ transmissions of the sidelink transport block include the first HARQ transmission of the sidelink transport block.

[0441] Example A23:

[0442] An apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processor, cause the apparatus to at least perform:

[0443] - receiving at least one HARQ transmission of a sidelink transport block from a transmitter, said HARQ transmission comprising destination identifier information indicating a destination identifier of a receiver, and

[0444] - at least if the at least one HARQ transmission has been successfully received,

[0445] - monitoring receiver HARQ feedback for the at least one HARQ transmission from the receiver to obtain a receiver HARQ feedback monitoring result, and

[0446] - determining a relay decision as to whether to relay data of the at least one HARQ transmission to the receiver based on the receiver HARQ feedback monitoring result.

[0447] Example A24:

[0448] The device according to claim A23, wherein

[0449] - Determining the relay decision comprises:

[0450] - If the receiver HARQ feedback monitoring result indicates discontinuous transmission (eg, HARQ DTX), determining to relay the at least one HARQ transmitted data to the receiver.

[0451] Example A25:

[0452] The device according to claim A23 or A24, wherein

[0453] - Determining the relay decision comprises:

[0454] - If the receiver HARQ feedback monitoring result indicates a negative acknowledgement (eg, HARQ NACK), determining to relay the at least one HARQ transmitted data to the receiver.

[0455] Example A26:

[0456] The apparatus of any one of embodiments A23 to A25, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0457] - If the at least one HARQ transmission is not successfully received, transmitting a relay HARQ feedback indicating a negative acknowledgement (eg, HARQ NACK) to the transmitter.

[0458] Example A27:

[0459] The apparatus of embodiment A26, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0460] - receiving at least one HARQ retransmission of the sidelink transport block from the transmitter after the transmission of the relay HARQ feedback message indicating the negative acknowledgement information.

[0461] Example A28:

[0462] The apparatus of any one of embodiments A23 to A27, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0463] - skipping transmission of relay HARQ feedback indicating a positive acknowledgement (eg, HARQ ACK) to the transmitter if the at least one HARQ transmission has been successfully received.

[0464] Example A29:

[0465] An apparatus according to any one of embodiments A23 to A28, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0466] - Relaying data of the at least one HARQ transmission or HARQ retransmission to the receiver based on the relay decision.

[0467] Example A30:

[0468] The apparatus of any one of embodiments A23 to A29, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform:

[0469] - monitoring a sidelink HARQ feedback for the relay data from the receiver to obtain a sidelink HARQ feedback monitoring result.

[0470] Example A31:

[0471] The apparatus of any one of embodiments A23 to A30, wherein the at least one HARQ transmission of the sidelink transport block is a first HARQ transmission of the sidelink transport block.

[0472] Example A32:

[0473] The apparatus according to any one of embodiments A23 to A31, wherein the apparatus is a mobile device and / or an Internet of Things (IoT) device, or is a part of a mobile device and / or an Internet of Things (IoT) device.

[0474] Example A33:

[0475] A system comprising:

[0476] - at least one device according to any one of embodiments A1 to A22; and

[0477] - at least one device according to any of embodiments A23 to A32.

[0478] Example M1:

[0479] A method comprising:

[0480] - transmitting at least one HARQ transmission of a sidelink transport block, the at least one HARQ transmission comprising destination identifier information indicating a destination identifier of a receiver,

[0481] - monitoring receiver HARQ feedback for the at least one HARQ transmission from the receiver to obtain a receiver HARQ feedback monitoring result,

[0482] - monitoring relay HARQ feedback for the at least one HARQ transmission from the relay device to obtain a relay HARQ feedback monitoring result, and

[0483] - determining a retransmission decision regarding whether to transmit at least one HARQ retransmission of the sidelink transport block based on the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result.

[0484] Example M2:

[0485] The method of embodiment M1, further comprising:

[0486] - transmitting the at least one HARQ retransmission according to the retransmission decision.

[0487] Example M3:

[0488] The method of embodiment M1 or M2, wherein:

[0489] - The HARQ retransmission includes destination identifier information indicating a destination identifier of the relay device.

[0490] Example M4:

[0491] The method of any one of embodiments M1 to M3, wherein:

[0492] - Determining the retransmission decision comprises:

[0493] - determining to retransmit the at least one HARQ retransmission at least if the receiver HARQ feedback monitoring result indicates discontinuous transmission (e.g., HARQ DTX) and the relay HARQ feedback monitoring result indicates negative acknowledgement (e.g., HARQ NACK).

[0494] Example M5:

[0495] The method of any one of embodiments M1 to M4, wherein:

[0496] - Transmitting the at least one HARQ transmission comprises:

[0497] - transmitting the at least one HARQ transmission as a multicast sidelink HARQ transmission.

[0498] Example M6:

[0499] The method of any one of embodiments M1 to M5, wherein:

[0500] - Transmitting the at least one HARQ retransmission comprises:

[0501] - transmitting the at least one HARQ retransmission as a unicast sidelink HARQ (re)transmission.

[0502] Example M7:

[0503] The method of any one of embodiments M1 to M6, wherein:

[0504] - Determining the retransmission decision comprises:

[0505] - in a case where the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate a negative acknowledgement (e.g., HARQ NACK),

[0506] A determination is made to transmit the at least one HARQ retransmission.

[0507] Example M8:

[0508] The method of any one of embodiments M1 to M7, wherein:

[0509] - Determining the retransmission decision comprises:

[0510] - in a case where the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate discontinuous transmission (e.g., HARQ DTX),

[0511] Determining not to transmit the at least one HARQ retransmission.

[0512] Example M9:

[0513] The method of any one of embodiments M1 to M8, further comprising:

[0514] - In a case where the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate discontinuous transmission (eg, HARQ DTX), terminating the HARQ process.

[0515] Example M10:

[0516] The method of any one of embodiments M1 to M9, wherein

[0517] - Determining the retransmission decision comprises:

[0518] - if the receiver HARQ feedback monitoring result indicates a negative acknowledgement (eg, HARQ NACK) and the relay HARQ feedback monitoring result indicates discontinuous transmission (eg, HARQ DTX), determining not to transmit the at least one HARQ retransmission.

[0519] Example M11:

[0520] The method of any one of embodiments M1 to M10, further comprising:

[0521] - If the receiver HARQ feedback monitoring result indicates negative acknowledgement (eg, HARQ NACK) and the relay HARQ feedback monitoring result indicates discontinuous transmission (eg, HARQ DTX), terminating the HARQ process.

[0522] Example M12:

[0523] The method of any one of embodiments M1 to M11, wherein

[0524] - Determining the retransmission decision comprises:

[0525] - If the receiver HARQ feedback monitoring result indicates a positive acknowledgement (eg, HARQ ACK), determining not to transmit the at least one HARQ retransmission.

[0526] Example M13:

[0527] The method of any one of embodiments M1 to M12, further comprising:

[0528] - If the receiver HARQ feedback monitoring result indicates a positive acknowledgement (eg, HARQ ACK), terminating the HARQ process.

[0529] Example M14:

[0530] The method of any one of embodiments M8 to M13, further comprising:

[0531] - Release the relay.

[0532] Example M15:

[0533] The method of any one of embodiments M1 to M14, further comprising:

[0534] - transmitting more than one consecutive HARQ transmission of said sidelink transport block,

[0535] - monitoring a corresponding receiver HARQ feedback for a corresponding HARQ transmission from the receiver to obtain a corresponding receiver HARQ feedback monitoring result, and

[0536] - monitoring corresponding relay HARQ feedback for corresponding HARQ transmission from the relay device to obtain corresponding relay HARQ feedback monitoring results,

[0537] - determining a respective retransmission decision regarding whether to transmit at least one respective HARQ retransmission of the sidelink transport block based on the respective receiver HARQ feedback monitoring result and the respective relay HARQ feedback monitoring result.

[0538] Example M16:

[0539] The method of any one of embodiments M1 to M15, further comprising:

[0540] - monitoring a message including sidelink control information (SCI) from the relay device to the receiver to obtain an SCI monitoring result,

[0541] - Optionally, determining a termination decision on whether to terminate the HARQ process according to the SCI monitoring result.

[0542] Example M17:

[0543] The method of any one of embodiments M1 to M16, further comprising:

[0544] - monitoring the sidelink HARQ feedback from the receiver to the relay to obtain SL HARQ feedback monitoring results, and

[0545] - Optionally, determining a release decision on whether to release the relay according to the SL HARQ feedback monitoring result.

[0546] Example M18:

[0547] The method of any one of embodiments M1 to M17, further comprising:

[0548] - monitoring the sidelink HARQ feedback from the receiver to the transmitter or to the relay device to obtain SLHARQ feedback monitoring results, and

[0549] -Release the relay device according to the SL HARQ feedback monitoring result.

[0550] Example M19:

[0551] The method of any one of embodiments M1 to M18, further comprising:

[0552] - performing a relay establishment procedure for establishing the relay device.

[0553] Example M20:

[0554] The method according to any one of embodiments M1 to M19, wherein the method is performed on or in conjunction with a mobile device and / or an Internet of Things (IoT) device.

[0555] Example M21:

[0556] The method of any one of embodiments M1 to M20, wherein the at least one HARQ transmission of the sidelink transport block is a first HARQ transmission of the sidelink transport block.

[0557] Example M22:

[0558] The method of embodiment M15, wherein the more than one consecutive HARQ transmissions of the sidelink transport block include the first HARQ transmission of the sidelink transport block.

[0559] Example M23:

[0560] A method comprising at least one processor and at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processor, cause the method to at least perform:

[0561] - receiving at least one HARQ transmission of a sidelink transport block from a transmitter, said HARQ transmission comprising destination identifier information indicating a destination identifier of a receiver, and

[0562] - at least if the at least one HARQ transmission has been successfully received,

[0563] - monitoring receiver HARQ feedback for the at least one HARQ transmission from the receiver to obtain a receiver HARQ feedback monitoring result, and

[0564] - determining a relay decision as to whether to relay data of the at least one HARQ transmission to the receiver based on the receiver HARQ feedback monitoring result.

[0565] Example M24:

[0566] The method according to claim M23, wherein

[0567] - Determining the relay decision comprises:

[0568] - If the receiver HARQ feedback monitoring result indicates discontinuous transmission (eg, HARQ DTX), determining to relay the at least one HARQ transmitted data to the receiver.

[0569] Example M25:

[0570] The method according to claim M23 or M24, wherein

[0571] - Determining the relay decision comprises:

[0572] - If the receiver HARQ feedback monitoring result indicates a negative acknowledgement (eg, HARQ NACK), determining to relay the at least one HARQ transmitted data to the receiver.

[0573] Example M26:

[0574] The method of any one of embodiments M23 to M25, further comprising:

[0575] - If the at least one HARQ transmission is not successfully received, transmitting a relay HARQ feedback indicating a negative acknowledgement (eg, HARQ NACK) to the transmitter.

[0576] Example M27:

[0577] The method of any one of embodiments M23 to M26, further comprising:

[0578] - receiving at least one HARQ retransmission of the sidelink transport block from the transmitter after the transmission of the relay HARQ feedback message indicating the negative acknowledgement information.

[0579] Example M28:

[0580] The method of any one of embodiments M23 to M27, further comprising:

[0581] - skipping transmission of relay HARQ feedback indicating a positive acknowledgement (eg, HARQ ACK) to the transmitter if the at least one HARQ transmission has been successfully received.

[0582] Example M29:

[0583] The method of any one of embodiments M23 to M28, further comprising:

[0584] - Relaying data of the at least one HARQ transmission or HARQ retransmission to the receiver based on the relay decision.

[0585] Example M30:

[0586] The method of any one of embodiments M23 to M29, further comprising:

[0587] - monitoring a sidelink HARQ feedback for the relay data from the receiver to obtain a sidelink HARQ feedback monitoring result.

[0588] Example M31:

[0589] The method of any one of embodiments M23 to M30, wherein the at least one HARQ transmission of the sidelink transport block is a first HARQ transmission of the sidelink transport block.

[0590] Example M32:

[0591] The method according to any one of embodiments M23 to M32, wherein the method is performed on or in conjunction with a mobile device and / or an Internet of Things (IoT) device.

[0592] Example C1:

[0593] A tangible computer-readable medium storing computer program code which, when executed by a processor, causes an apparatus to perform and / or control:

[0594] - transmitting at least one HARQ transmission of a sidelink transport block, the at least one HARQ transmission comprising destination identifier information indicating a destination identifier of a receiver,

[0595] - monitoring receiver HARQ feedback for the at least one HARQ transmission from the receiver to obtain a receiver HARQ feedback monitoring result,

[0596] - monitoring relay HARQ feedback for the at least one HARQ transmission from the relay device to obtain a relay HARQ feedback monitoring result, and

[0597] - determining a retransmission decision regarding whether to transmit at least one HARQ retransmission of the sidelink transport block based on the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result.

[0598] Example C2:

[0599] The tangible computer readable medium of embodiment C1, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0600] - transmitting the at least one HARQ retransmission according to the retransmission decision.

[0601] Example C3:

[0602] The tangible computer readable medium of embodiment C1 or C2, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0603] - The HARQ retransmission includes destination identifier information indicating a destination identifier of the relay device.

[0604] Example C4:

[0605] The tangible computer readable medium according to any one of embodiments C1 to C3, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0606] - Determining the retransmission decision comprises:

[0607] - determining to retransmit the at least one HARQ retransmission at least if the receiver HARQ feedback monitoring result indicates discontinuous transmission (e.g., HARQ DTX) and the relay HARQ feedback monitoring result indicates negative acknowledgement (e.g., HARQ NACK).

[0608] Example C5:

[0609] The tangible computer readable medium according to any one of embodiments C1 to C4, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0610] - Transmitting the at least one HARQ transmission comprises:

[0611] - transmitting the at least one HARQ transmission as a multicast sidelink HARQ transmission.

[0612] Example C6:

[0613] The tangible computer readable medium according to any one of embodiments C1 to C5, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0614] - Transmitting the at least one HARQ retransmission comprises:

[0615] - transmitting the at least one HARQ retransmission as a unicast sidelink HARQ (re)transmission.

[0616] Example C7:

[0617] The tangible computer readable medium according to any one of embodiments C1 to C6, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0618] - Determining the retransmission decision comprises:

[0619] - in a case where the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate a negative acknowledgement (e.g., HARQ NACK),

[0620] A determination is made to transmit the at least one HARQ retransmission.

[0621] Example C8:

[0622] The tangible computer readable medium according to any one of embodiments C1 to C7, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0623] - Determining the retransmission decision comprises:

[0624] - in a case where the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate discontinuous transmission (e.g., HARQ DTX),

[0625] Determining not to transmit the at least one HARQ retransmission.

[0626] Example C9:

[0627] The tangible computer readable medium according to any one of embodiments C1 to C8, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0628] - In a case where the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate discontinuous transmission (eg, HARQ DTX), terminating the HARQ process.

[0629] Example C10:

[0630] The tangible computer readable medium according to any one of embodiments C1 to C9, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0631] - Determining the retransmission decision comprises:

[0632] - if the receiver HARQ feedback monitoring result indicates a negative acknowledgement (eg, HARQ NACK) and the relay HARQ feedback monitoring result indicates discontinuous transmission (eg, HARQ DTX), determining not to transmit the at least one HARQ retransmission.

[0633] Example C11:

[0634] The tangible computer readable medium according to any one of embodiments C1 to C10, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0635] - If the receiver HARQ feedback monitoring result indicates negative acknowledgement (eg, HARQ NACK) and the relay HARQ feedback monitoring result indicates discontinuous transmission (eg, HARQ DTX), terminating the HARQ process.

[0636] Example C12:

[0637] The tangible computer readable medium according to any one of embodiments C1 to C11, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0638] - Determining the retransmission decision comprises:

[0639] - If the receiver HARQ feedback monitoring result indicates a positive acknowledgement (eg, HARQ ACK), determining not to transmit the at least one HARQ retransmission.

[0640] Example C13:

[0641] The tangible computer readable medium according to any one of embodiments C1 to C12, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0642] - If the receiver HARQ feedback monitoring result indicates a positive acknowledgement (eg, HARQ ACK), terminating the HARQ process.

[0643] Example C14:

[0644] The tangible computer readable medium according to any one of embodiments C8 to C13, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0645] - releasing the relay device.

[0646] Example C15:

[0647] The tangible computer readable medium according to any one of embodiments C1 to C14, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0648] - transmitting more than one consecutive HARQ transmission of said sidelink transport block,

[0649] - monitoring a corresponding receiver HARQ feedback for a corresponding HARQ transmission from the receiver to obtain a corresponding receiver HARQ feedback monitoring result, and

[0650] - monitoring corresponding relay HARQ feedback for corresponding HARQ transmission from the relay device to obtain corresponding relay HARQ feedback monitoring results,

[0651] - determining a respective retransmission decision regarding whether to transmit at least one respective HARQ retransmission of the sidelink transport block based on the respective receiver HARQ feedback monitoring result and the respective relay HARQ feedback monitoring result.

[0652] Example C16:

[0653] The tangible computer readable medium according to any one of embodiments C1 to C15, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0654] - monitoring a message including sidelink control information (SCI) from the relay device to the receiver to obtain an SCI monitoring result,

[0655] - Optionally, determining a termination decision on whether to terminate the HARQ process according to the SCI monitoring result.

[0656] Example C17:

[0657] The tangible computer readable medium according to any one of embodiments C1 to C16, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0658] - monitoring the sidelink HARQ feedback from the receiver to the relay to obtain SL HARQ feedback monitoring results, and

[0659] - Optionally, determining a release decision on whether to release the relay according to the SL HARQ feedback monitoring result.

[0660] Example C18:

[0661] The tangible computer readable medium according to any one of embodiments C1 to C17, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0662] - monitoring the sidelink HARQ feedback from the receiver to the transmitter or to the relay device to obtain SLHARQ feedback monitoring results, and

[0663] -Release the relay device according to the SL HARQ feedback monitoring result.

[0664] Example C19:

[0665] The tangible computer readable medium according to any one of embodiments C1 to C18, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0666] --Execute the relay establishment process for establishing the relay device.

[0667] Example C20:

[0668] The tangible computer readable medium according to any one of embodiments C1 to C19, wherein the apparatus is a mobile device and / or an Internet of Things (IoT) device.

[0669] Example C21:

[0670] The apparatus of any one of embodiments C1 to C20, wherein the at least one HARQ transmission of the sidelink transport block is a first HARQ transmission of the sidelink transport block.

[0671] Example C22:

[0672] The apparatus of embodiment C15, wherein the more than one consecutive HARQ transmissions of the sidelink transport block include the first HARQ transmission of the sidelink transport block.

[0673] Example C23:

[0674] A tangible computer-readable medium storing computer program code which, when executed by a processor, causes an apparatus to perform and / or control:

[0675] - receiving at least one HARQ transmission of a sidelink transport block from a transmitter, said HARQ transmission comprising destination identifier information indicating a destination identifier of a receiver, and

[0676] - at least if the at least one HARQ transmission has been successfully received,

[0677] - monitoring receiver HARQ feedback for the at least one HARQ transmission from the receiver to obtain a receiver HARQ feedback monitoring result, and

[0678] - determining a relay decision as to whether to relay data of the at least one HARQ transmission to the receiver based on the receiver HARQ feedback monitoring result.

[0679] Example C24:

[0680] The tangible computer-readable medium according to claim C23, wherein the computer program code, when executed by a processor, causes the device to perform and / or control:

[0681] - Determining the relay decision comprises:

[0682] - If the receiver HARQ feedback monitoring result indicates discontinuous transmission (eg, HARQ DTX), determining to relay the at least one HARQ transmitted data to the receiver.

[0683] Example C25:

[0684] The tangible computer-readable medium according to claim C23 or C24, wherein the computer program code, when executed by a processor, causes the device to perform and / or control:

[0685] - Determining the relay decision comprises:

[0686] - If the receiver HARQ feedback monitoring result indicates a negative acknowledgement (eg, HARQ NACK), determining to relay the at least one HARQ transmitted data to the receiver.

[0687] Example C26:

[0688] The tangible computer-readable medium according to any one of embodiments C23 to C25, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0689] - If the at least one HARQ transmission is not successfully received, transmitting a relay HARQ feedback indicating a negative acknowledgement (eg, HARQ NACK) to the transmitter.

[0690] Example C27:

[0691] According to the tangible computer readable medium of embodiment C26, the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0692] - receiving at least one HARQ retransmission of the sidelink transport block from the transmitter after the transmission of the relay HARQ feedback message indicating the negative acknowledgement information.

[0693] Example C28:

[0694] The tangible computer readable medium according to any one of embodiments C23 to C27, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0695] - skipping transmission of relay HARQ feedback indicating a positive acknowledgement (eg, HARQ ACK) to the transmitter if the at least one HARQ transmission has been successfully received.

[0696] Example C29:

[0697] The tangible computer readable medium according to any one of embodiments C23 to C28, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0698] - Relaying data of the at least one HARQ transmission or HARQ retransmission to the receiver based on the relay decision.

[0699] Example C30:

[0700] The tangible computer-readable medium according to any one of embodiments C23 to C29, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0701] - monitoring a sidelink HARQ feedback for the relay data from the receiver to obtain a sidelink HARQ feedback monitoring result.

[0702] Example C31:

[0703] The tangible computer-readable medium according to any one of embodiments C23 to C30, wherein the computer program code, when executed by a processor, causes an apparatus to perform and / or control:

[0704] - The at least one HARQ transmission of the sidelink transport block is a first HARQ transmission of the sidelink transport block.

[0705] Example C32:

[0706] The tangible computer-readable medium of any one of embodiments C23 to C31, wherein the apparatus is a mobile device and / or an Internet of Things (IoT) device.

[0707] Example G1:

[0708] An apparatus comprises at least one processor and at least one memory comprising computer program code, wherein the at least one memory and the computer program code are configured to, together with the at least one processor, cause the apparatus to at least perform and / or control the method of the first exemplary aspect.

[0709] Thus, the example embodiments may be used to implement the enhancements and solutions necessary to support high accuracy (e.g., horizontal and / or vertical), low latency, network efficiency (scalability, RS overhead, etc.), and device efficiency (power consumption, complexity) requirements for business use cases, including general business use cases and specifically (I)IoT use cases.

[0710] In this specification, any connection presented in the described embodiments should be understood in a manner that the components involved are operatively coupled. Therefore, the connection can be direct or indirect with any number or combination of intermediate elements, and there can only be a functional relationship between the components.

[0711] Furthermore, any methods, processes, and actions described or illustrated herein may be implemented using executable instructions in a general-purpose or special-purpose processor, the executable instructions being stored on a computer-readable storage medium (e.g., disk, memory, etc.) for execution by such a processor. References to "computer-readable storage medium" should be understood to encompass special-purpose circuits such as FPGAs, ASICs, signal processing devices, and other devices.

[0712] The expression "A and / or B" is considered to include any of the following three situations: (i) A, (ii) B, and (iii) A and B. In addition, the article "a" should not be understood as meaning "one," that is, the use of the expression "an element" does not exclude the presence of other elements. The term "comprising" should be understood in an open manner, that is, the object of "comprising element A" may include other elements in addition to element A.

[0713] It should be understood that all presented embodiments are exemplary and that any feature presented for a particular example embodiment may be used with any aspect of the present invention alone or in combination with any feature presented for the same or another particular example embodiment and / or in combination with any other feature not mentioned. In particular, the example embodiments presented in this specification should also be understood to be disclosed in all possible combinations with each other, as long as they are technically reasonable and the example embodiments are not alternatives to each other. It should also be understood that any feature presented for an example embodiment of a particular category (method / apparatus / computer program / system) may also be used in a corresponding manner in example embodiments of any other category. It should also be understood that the presence of a feature in a presented example embodiment does not necessarily mean that the feature forms an essential feature of the invention and cannot be omitted or replaced.

[0714] The statement that a feature includes at least one of the subsequently listed features is not mandatory for the feature to include all of the subsequently listed features or at least one of a plurality of the subsequently listed features. Furthermore, any combination of the listed features or one of the listed features can be selected. Specific combinations of all of the subsequently listed features are also conceivable. Furthermore, multiple occurrences of one of the listed features are possible.

[0715] The sequence of all the above method steps is not mandatory, and other sequences may be adopted. However, the specific sequence of the method steps exemplarily shown in the figures should be regarded as a possible sequence of the method steps of the corresponding embodiment described by the corresponding figure.

[0716] The present invention has been described above by way of example embodiments. It should be noted that there are alternatives and modifications that are obvious to those skilled in the art and that can be implemented without departing from the scope of the appended claims.

[0717] By utilizing the present invention and its various aspects described herein, for example, one or more of the following may be achieved:

[0718] - facilitating SL data transmission of a unicast SL between a transmitter (e.g., Tx UE) and a receiver (e.g., Rx UE) using SL-based UE-to-UE relay via a relay device (e.g., R-UE); and

[0719] - Enable and facilitate seamless return from current UE-to-UE relay mode to direct SL mode once direct SL mode is applicable again for unicast SL for both transmitter (e.g., Tx UE) and receiver (e.g., Rx UE).

Claims

1. An apparatus for communication, comprising at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, together with the at least one processor, cause the apparatus to at least perform: - transmitting at least one HARQ transmission of a sidelink transport block, the at least one HARQ transmission comprising destination identifier information indicating a destination identifier of a receiver, - monitoring receiver HARQ feedback for the at least one HARQ transmission from the receiver to obtain a receiver HARQ feedback monitoring result, - monitoring relay HARQ feedback for the at least one HARQ transmission from the relay device to obtain a relay HARQ feedback monitoring result, and - determining a retransmission decision regarding whether to transmit at least one HARQ retransmission of the sidelink transport block based on the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result, in: - Determining that the retransmission decision comprises at least one of the following: - if the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate discontinuous transmission, determining not to transmit the at least one HARQ retransmission; - if the receiver HARQ feedback monitoring result indicates a negative acknowledgement and the relay HARQ feedback monitoring result indicates a discontinuous transmission, determining not to transmit the at least one HARQ retransmission.

2. The apparatus of claim 1 , wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform: - transmitting the at least one HARQ retransmission depending on the retransmission decision.

3. The device according to claim 1 or 2, wherein: - The HARQ retransmission includes destination identifier information indicating a destination identifier of the relay device.

4. The device according to claim 1 or 2, wherein: - Transmitting the at least one HARQ transmission comprises: - transmitting the at least one HARQ transmission as a multicast sidelink HARQ transmission.

5. The device according to claim 1 or 2, wherein: - Determining the retransmission decision comprises: - determining to transmit the at least one HARQ retransmission at least if the receiver HARQ feedback monitoring result indicates discontinuous transmission and the relay HARQ feedback monitoring result indicates negative acknowledgement.

6. The device according to claim 1 or 2, wherein: - Determining the retransmission decision comprises: - if the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate a negative acknowledgement, determining to transmit the at least one HARQ retransmission.

7. The device according to claim 1 or 2, wherein: - Transmitting the at least one HARQ retransmission comprises: - transmitting the at least one HARQ retransmission as a unicast sidelink HARQ retransmission.

8. The device according to claim 1 or 2, wherein - Determining the retransmission decision comprises: - if the receiver HARQ feedback monitoring result indicates a positive acknowledgement, determining not to transmit the at least one HARQ retransmission.

9. The apparatus of claim 8, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform: - terminating the HARQ process.

10. The apparatus of claim 8, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform: - Release the relay.

11. The apparatus according to claim 1 or 2, wherein the at least one memory and the computer program code are configured to, together with the at least one processor, cause the apparatus to further perform: - transmitting more than one consecutive HARQ transmission of said sidelink transport block, - monitoring corresponding receiver HARQ feedback for corresponding HARQ transmission from the receiver to obtain corresponding receiver HARQ feedback monitoring results, - monitoring corresponding relay HARQ feedback for corresponding HARQ transmission from the relay device to obtain corresponding relay HARQ feedback monitoring results, - determining a corresponding retransmission decision regarding whether to transmit at least one corresponding HARQ retransmission of the sidelink transport block based on the corresponding receiver HARQ feedback monitoring result and the corresponding relay HARQ feedback monitoring result.

12. An apparatus for communication, comprising at least one processor and at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processor, cause the apparatus to at least perform: - receiving at least one HARQ transmission of a sidelink transport block from a transmitter, the at least one HARQ transmission comprising destination identifier information indicating a destination identifier for a receiver, and - at least if the at least one HARQ transmission has been successfully received, - monitoring receiver HARQ feedback from the receiver for the at least one HARQ transmission to obtain a receiver HARQ feedback monitoring result, and - determining a relay decision as to whether to relay data of the at least one HARQ transmission to the receiver based on the receiver HARQ feedback monitoring result, in: - Determining the relay decision comprises: - If the receiver HARQ feedback monitoring result indicates discontinuous transmission, determining to relay the at least one HARQ transmitted data to the receiver.

13. The device according to claim 12, wherein - Determining the relay decision comprises: - If the receiver HARQ feedback monitoring result indicates a negative acknowledgement, determining to relay the at least one HARQ transmitted data to the receiver.

14. A method for communication, comprising: - transmitting at least one HARQ transmission of a sidelink transport block, the at least one HARQ transmission comprising destination identifier information indicating a destination identifier of a receiver, - monitoring receiver HARQ feedback for the at least one HARQ transmission from the receiver to obtain a receiver HARQ feedback monitoring result, - monitoring relay HARQ feedback for the at least one HARQ transmission from the relay device to obtain a relay HARQ feedback monitoring result, and - determining a retransmission decision regarding whether to transmit at least one HARQ retransmission of the sidelink transport block based on the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result, in: - Determining that the retransmission decision comprises at least one of the following: - if the receiver HARQ feedback monitoring result and the relay HARQ feedback monitoring result each indicate discontinuous transmission, determining not to transmit the at least one HARQ retransmission, and - if the receiver HARQ feedback monitoring result indicates a negative acknowledgement and the relay HARQ feedback monitoring result indicates a discontinuous transmission, determining not to transmit the at least one HARQ retransmission.

15. A method for communication, comprising: - receiving at least one HARQ transmission of a sidelink transport block from a transmitter, the at least one HARQ transmission comprising destination identifier information indicating a destination identifier for a receiver, and - at least if the at least one HARQ transmission has been successfully received, - monitoring receiver HARQ feedback from the receiver for the at least one HARQ transmission to obtain a receiver HARQ feedback monitoring result, and - determining a relay decision as to whether to relay data of the at least one HARQ transmission to the receiver based on the receiver HARQ feedback monitoring result, in: - Determining the relay decision comprises: - If the receiver HARQ feedback monitoring result indicates discontinuous transmission, determining to relay the at least one HARQ transmitted data to the receiver.

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