WO2022148832A1

WO2022148832A1 - Methods and devices for sidelink transmissions

Info

Publication number: WO2022148832A1
Application number: PCT/EP2022/050250
Authority: WO
Inventors: Min Wang
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2021-01-08
Filing date: 2022-01-07
Publication date: 2022-07-14
Also published as: EP4275432A1

Abstract

A method implemented by a first terminal device is provided. The method comprises: transmitting, to a control node, a first signaling indicating that the first terminal device has pending transmissions on a sidelink towards a second terminal device; receiving a sidelink grant from the control node; and initiating transmissions on the sidelink to the second terminal device based on the sidelink grant. Latency, power consumption and signaling overhead may be reduced. Data loss due to active time misalignment may be minimized. A good tradeoff between UE power consumption and performance of sidelink transmissions may be achieved.

Description

METHODS AND DEVICES FOR SIDELINK TRANSMISSIONS

TECHNICAL FIELD

The present disclosure generally relates to the field of sidelink transmissions, and more particularly to methods and devices for alignment of active time in the sidelink transmissions.

BACKGROUND

This section introduces aspects that may facilitate better understanding of the present disclosure. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.

NR frame structure

Similar to LTE (Long-Term Evolution), NR (New Radio) uses OFDM (Orthogonal Frequency Division Multiplexing) in the downlink (i.e. from a network node, gNB, eNB, or base station, to a user equipment or UE). The basic NR physical resource over an antenna port may be seen as a time-frequency grid as illustrated in Fig. 1, where a resource block (RB) in a 14-symbol slot is shown. The resource block corresponds to 12 contiguous subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth. Each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval.

Different subcarrier spacing values are supported in NR. The supported subcarrier spacing values (also referred to as different numerologies) are given by Dί=(15^c2^Lm) kHz where

(0,1, 2, 3, 4). Dί=T5 kHz is the basic (or reference) subcarrier spacing that is also used in LTE.

In the time domain, downlink and uplink transmissions in NR may be organized into equally-sized subframes of 1ms each similar to LTE. A subframe is further divided into multiple slots of equal duration. The slot length for subcarrier spacing Dί=(15^c2^Lm) kHz is 1/2^Lm ms. There is only one slot per subframe for Af=15 kHz and a slot consists of 14 OFDM symbols.

Downlink transmissions are dynamically scheduled, i.e., in each slot, the gNB transmits downlink control information (DCI) about which UE data is to be transmitted to and which resource blocks in the current downlink slot the data is transmitted on. This control information is typically transmitted in the first one or two OFDM symbols in each slot in NR. The control information is carried on the Physical Control Channel (PDCCH) and data is carried on the Physical Downlink Shared Channel (PDSCH). A UE first detects and decodes a PDCCH, and if a PDCCH is decoded successfully, the UE then decodes the corresponding PDSCH based on the downlink assignment provided by decoded control information in the PDCCH.

In addition to the PDCCH and the PDSCH, there are also other channels and reference signals transmitted in the downlink, including SSB, CSI-RS, etc.

Uplink data transmissions, carried on the Physical Uplink Shared Channel (PUSCH), may also be dynamically scheduled by the gNB by transmitting DCI. The DCI (which is transmitted in the downlink region) always indicates a scheduling time offset so that the PUSCH is transmitted in a slot in the uplink region.

Sidelink transmissions in NR

Sidelink transmissions over New Radio (NR) are specified in the 3rd Generation Partnership Project in Release 16, including enhancements of Proximity-based Services (ProSe) specified for Long Term Evolution (LTE). Four new enhancements are particularly introduced to NR sidelink transmissions as follows:

^• Support for unicast and groupcast transmissions is added in NR sidelink. For unicast and groupcast, a Physical Sidelink Feedback Channel (PSFCH) is introduced for a receiver User Equipment (UE) to reply a decoding status to a transmitter UE. ^• Grant-free transmissions, which are adopted in NR uplink transmissions, are also provided in NR sidelink transmissions, to improve the latency performance.

• To alleviate resource collisions among different sidelink transmissions launched by different UEs, it enhances channel sensing and resource selection procedures, which also leads to a new design of Physical Sidelink Common Control Channel (PSCCH).

^• To achieve a high connection density, congestion control and thus QoS management are supported in NR sidelink transmissions.

To enable the above enhancements, new physical channels and reference signals are introduced in NR:

^• Physical Sidelink Shared Channel (PSSCH), a sidelink version of Physical Downlink Shared Channel (PDSCH): The PSSCH is transmitted by a sidelink transmitter UE, and conveys sidelink transmission data, System Information Blocks (SIBs) for Radio Resource Control (RRC) configuration, and a part of Sidelink Control Information (SCI), a sidelink version of Downlink Control Information (DCI).

• PSFCH, a sidelink version of Physical Uplink Control Channel (PUCCH): The PSFCH is transmitted by a sidelink receiver UE for unicast and groupcast, and conveys 1 bit information over 1 Resource Block (RB) for a Hybrid Automatic Repeat reQeust (HARQ) acknowledgement (ACK) or a negative ACK (NACK). In addition, Channel State Information (CSI) is carried in a Medium Access Control (MAC) Control Element (CE) over the PSSCH instead of the PSFCH.

^• PSCCH, a sidelink version of Physical Downlink Control Channel (PDCCH): When traffic to be sent to a receiver UE arrives at a transmitter UE, the transmitter UE should first send the PSCCH, which conveys a part of SCI to be decoded by any UE for the channel sensing purpose, including reserved time-frequency resources for transmissions, DeModulation Reference Signal (DMRS) pattern, and antenna port, etc.

•Sidelink Primary/Secondary Synchronization Signal (S-PSS/S-SSS): Similar to downlink transmissions in NR, in sidelink transmissions, S-PSS and S-SSS are supported. Through detecting the S-PSS and S-SSS, a UE is able to identify a Sidelink Synchronization Identity (SSID) from the UE sending the S-PSS/S-SSS. The UE is therefore able to know the characteristics of the transmitter UE from the S-PSS/S-SSS. A series of processes of acquiring timing and frequency synchronization together with SSIDs of UEs is called initial cell search. Note that the UE sending the S-PSS/S-SSS may not be necessarily involved in sidelink transmissions, and a node (e.g., UE, evolved NodeB (eNB), or (next) generation NodeB (gNB)) sending the S-PSS/S-SSS is called a synchronization source. There are 2 S-PSS sequences and 336 S-SSS sequences forming a total of 672 SSIDs in a cell.

• Physical Sidelink Broadcast Channel (PSBCH): The PSBCH is transmitted along with the S-PSS/S-SSS as a Synchronization Signal/PSBCH Block (SSB). The SSB has the same numerology as PSCCH/PSSCH on the carrier, and an SSB should be transmitted within the bandwidth of the configured BWP. The PSBCH conveys information related to synchronization, such as the Direct Frame Number (DFN), an indication of the slot and symbol level time resources for sidelink transmissions, an in-coverage indicator, etc. The SSB is transmitted periodically at every 160 ms.

• DMRS, Phase Tracking Reference Signal (PT-RS), Channel State Information Reference Signal (CSI-RS): These physical reference signals supported by NR downlink/uplink transmissions are also adopted by sidelink transmissions. Similarly, the PT-RS is only applicable for Frequency Range 2 (FR2) transmission.

SUMMARY

An object of the present disclosure is to provide methods and devices for alignment of active time in the sidelink (SL) transmissions.

According to a first aspect of the present disclosure, a method implemented by a first terminal device is provided. The method comprises: transmitting, to a control node, a first signaling indicating that the first terminal device has pending transmissions on a sidelink towards a second terminal device; receiving a sidelink grant from the control node; and initiating transmissions on the sidelink to the second terminal device based on the sidelink grant.

In an alternative embodiment of the first aspect, the first signaling may be transmitted via at least one of: a scheduling request, SR, on a physical uplink control channel, PUCCH; a buffer status report on a physical uplink shared channel, PUSCH; a random access channel, RACH, transmission; a non-SR transmission on the PUCCH; and a sounding reference signal, SRS, transmission.

In another alternative embodiment of the first aspect, the method may further comprise: transmitting, to the second terminal device, a second signaling indicating that the first terminal device has the pending sidelink transmissions towards the second terminal device.

In a further alternative embodiment of the first aspect, configurations of the first terminal device and the second terminal device are signaled by the control node or preconfigured.

According to a second aspect of the present disclosure, a method implemented by a control node is provided. The method comprises: receiving, from a first terminal device, a first signaling indicating that the first terminal device has pending transmissions on a sidelink towards a second terminal device; and transmitting a sidelink grant to the first terminal device.

According to a third aspect of the present disclosure, a method implemented by a second terminal device is provided. The method comprises: receiving a signaling indicating that a first terminal device has pending transmissions on a sidelink towards the second terminal device; entering an active state; and receiving transmissions on the sidelink from the first terminal device.

According to a fourth aspect of the present disclosure, a first terminal device is provided. The first terminal device comprises a processor and a memory communicatively coupled to the processor. The memory is adapted to store instructions which, when executed by the processor, cause the first terminal device to perform operations of the method according to the above first aspect.

According to a fifth aspect of the present disclosure, a first terminal device is provided. The first terminal device comprises at least a transmission unit, a receiving unit and an initiation unit. The transmission unit is adapted to transmit, to a control node, a first signaling indicating that the first terminal device has pending transmissions on a sidelink towards a second terminal device. The receiving unit is adapted to receive a sidelink grant from the control node. The initiation unit is adapted to initiate transmissions on the sidelink to the second terminal device based on the sidelink grant.

According to a sixth aspect of the present disclosure, a control node is provided. The control node comprises a processor and a memory communicatively coupled to the processor. The memory is adapted to store instructions which, when executed by the processor, cause the control node to perform operations of the method according to the above second aspect.

According to a seventh aspect of the present disclosure, a control node is provided. The control node comprises at least a receiving unit and a transmission. The receiving unit is adapted to receive, from a first terminal device, a first signaling indicating that the first terminal device has pending transmissions on a sidelink towards a second terminal device. The transmission unit is adapted to transmit a sidelink grant to the first terminal device.

According to an eighth aspect of the present disclosure, a second terminal device is provided. The second terminal device comprises a processor and a memory communicatively coupled to the processor. The memory is adapted to store instructions which, when executed by the processor, cause the second terminal device to perform operations of the method according to the above third aspect.

According to a ninth aspect of the present disclosure, a second terminal device is provided. The second terminal device comprises at least a receiving unit and an entering unit. The receiving unit is adapted to receive a signaling indicating that a first terminal device has pending transmissions on a sidelink towards the second terminal device and receive transmissions on the sidelink from the first terminal device. The entering unit is adapted to enter an active state.

According to a tenth aspect of the present disclosure, a wireless communication system is provided. The wireless communication system comprises: a first terminal device according to the above fourth or fifth aspect; a control node according to the above sixth or seventh aspect communicating with at least the first terminal device; and a second terminal device according to the above eighth or ninth aspect communicating with at least the first terminal device and the control node.

According to an eleventh aspect of the present disclosure, a non-transitory computer readable medium having a computer program stored thereon is provided. When the computer program is executed by a set of one or more processors of a first terminal device, the computer program causes the first terminal device to perform operations of the method according to the above first aspect.

According to a twelfth aspect of the present disclosure, a non-transitory computer readable medium having a computer program stored thereon is provided. When the computer program is executed by a set of one or more processors of a control node, the computer program causes the control node to perform operations of the method according to the above second aspect.

According to a thirteenth aspect of the present disclosure, a non-transitory computer readable medium having a computer program stored thereon is provided. When the computer program is executed by a set of one or more processors of a second terminal device, the computer program causes the second terminal device to perform operations of the method according to the above third aspect.

With the methods and devices of the present disclosure, latency, power consumption and signaling overhead may be reduced. Active time on the sidelink may be aligned between a transmitter (TX) UE with Mode 1 sidelink grant and another UE. In this way, data loss due to active time misalignment may be minimized. A good tradeoff between UE power consumption and performance of sidelink transmissions may be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be best understood by way of example with reference to the following description and accompanying drawings that are used to illustrate embodiments of the present disclosure. In the drawings:

Fig. 1 is a diagram illustrating an NR physical resource grid;

Fig. 2 is a diagram illustrating a procedure for a gNB to inform a receiver (RX) UE that a TX UE has pending SL transmissions;

Fig. 3 is a diagram illustrating a procedure for a TX UE to inform an RX UE that the TX UE has pending SL transmissions;

Fig. 4 is a diagram illustrating a procedure for a gNB to inform an RX UE via inter-gNB signaling indicating that a TX UE has pending SL transmissions;

Fig. 5 is a flow chart illustrating a method implemented on a first terminal device according to some embodiments of the present disclosure;

Fig. 6 is a flow chart illustrating a method implemented on a control node according to some embodiments of the present disclosure;

Fig. 7 is a flow chart illustrating a method implemented on a second terminal device according to some embodiments of the present disclosure;

Fig. 8 is a block diagram illustrating a first terminal device according to some embodiments of the present disclosure;

Fig. 9 is another block diagram illustrating a first terminal device according to some embodiments of the present disclosure;

Fig. 10 is a block diagram illustrating a control node according to some embodiments of the present disclosure;

Fig. 11 is another block diagram illustrating a control node according to some embodiments of the present disclosure;

Fig. 12 is a block diagram illustrating a second terminal device according to some embodiments of the present disclosure;

Fig. 13 is another block diagram illustrating a second terminal device according to some embodiments of the present disclosure;

Fig. 14 is a block diagram illustrating a wireless communication system according to some embodiments of the present disclosure;

Fig. 15 is a block diagram schematically illustrating a telecommunication network connected via an intermediate network to a host computer;

Fig. 16 is a generalized block diagram of a host computer communicating via a base station with a user equipment over a partially wireless connection; and

Figs. 17 to 20 are flowcharts illustrating methods implemented in a communication system including a host computer, a base station and a user equipment.

DETAILED DESCRIPTION

The following detailed description describes methods and devices for alignment of active time in the sidelink transmissions. In the following detailed description, numerous specific details such as logic implementations, types and interrelationships of system components, etc. are set forth in order to provide a more thorough understanding of the present disclosure. It should be appreciated, however, by one skilled in the art that the present disclosure may be practiced without such specific details. In other instances, control structures, circuits and instruction sequences have not been shown in detail in order not to obscure the present disclosure. Those of ordinary skill in the art, with the included descriptions, will be able to implement appropriate functionality without undue experimentation.

References in the specification to “one embodiment”, “an embodiment”, “an example embodiment” etc. indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

Bracketed text and blocks with dashed borders (e.g., large dashes, small dashes, dot-dash, and dots) may be used herein to illustrate optional operations that add additional features to embodiments of the present disclosure. However, such notation should not be taken to mean that these are the only options or optional operations, and/or that blocks with solid borders are not optional in certain embodiments of the present disclosure.

In the following detailed description and claims, the terms “coupled” and “connected,” along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. “Coupled” is used to indicate that two or more elements, which may or may not be in direct physical or electrical contact with each other, cooperate or interact with each other. “Connected” is used to indicate the establishment of communication between two or more elements that are coupled with each other.

An electronic device stores and transmits (internally and/or with other electronic devices over a network) code (which is composed of software instructions and which is sometimes referred to as computer program code or a computer program) and/or data using machine-readable media (also called computer-readable media), such as machine-readable storage media (e.g., magnetic disks, optical disks, read only memory (ROM), flash memory devices, phase change memory) and machine-readable transmission media (also called a carrier) (e.g., electrical, optical, radio, acoustical or other forms of propagated signals - such as carrier waves, infrared signals). Thus, an electronic device (e.g., a computer) includes hardware and software, such as a set of one or more processors coupled to one or more machine-readable storage media to store code for execution on the set of processors and/or to store data. For instance, an electronic device may include non-volatile memory containing the code since the non-volatile memory can persist code/data even when the electronic device is turned off (when power is removed), and while the electronic device is turned on, that part of the code that is to be executed by the processor(s) of that electronic device is typically copied from the slower non-volatile memory into volatile memory (e.g., dynamic random access memory (DRAM), static random access memory (SRAM)) of that electronic device. Typical electronic devices also include a set of one or more physical network interfaces to establish network connections (to transmit and/or receive code and/or data using propagating signals) with other electronic devices. One or more parts of an embodiment of the present disclosure may be implemented using different combinations of software, firmware, and/or hardware.

For sidelink transmissions in NR, two-stage sidelink control information (SCI) is introduced. This is a version of DCI for SL. Unlike the DCI, only part (first stage) of the SCI is sent on the PSCCH. This part is used for channel sensing purposes (including the reserved time-frequency resources for transmissions, demodulation reference signal (DMRS) pattern and antenna port, etc.) and may be read by all UEs while the remaining (second stage) scheduling and control information such as an 8-bit source identity (ID) and a 16-bit destination ID, a new data indicator (NDI), a redundancy version (RV) and a HARQ process ID is sent on the PSSCH to be decoded by the receiver UE.

Similar to PRoSe in LTE, NR sidelink transmissions have the following two modes of resource allocations:

^• Mode 1 : Sidelink resources are scheduled by a gNB.

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

For an in-coverage UE, a gNB may be configured to adopt Mode 1 or Mode 2. For an out-of-coverage UE, only Mode 2 may be adopted.

As in LTE, scheduling over the sidelink in NR is performed in different ways for Mode 1 and Mode 2. Mode 1 supports the following two types of grants:

Dynamic grant: When the traffic to be sent over the sidelink arrives at a transmitter UE, this UE should launch a four-message exchange procedure to request sidelink resources from a gNB (SR on uplink (UL), grant, buffer status report (BSR) on UL, grant for data on SL sent to UE). During the resource request procedure, a gNB may allocate a sidelink radio network temporary identifier (SL-RNTI) to the transmitter UE. If this sidelink resource request is granted by a gNB, then the gNB indicates the resource allocation for the PSCCH and the PSSCH in the DCI conveyed by the PDCCH with cyclic redundancy check (CRC) scrambled with the SL-RNTI. When the transmitter UE receives such DCI, the transmitter UE may obtain the grant only if the scrambled CRC of the DCI may be successfully solved by the assigned SL-RNTI. The transmitter UE then indicates time- frequency resources and a transmission scheme of the allocated PSSCH in the PSCCH, and launches the PSCCH and the PSSCH on the allocated resources for the sidelink transmissions. When a grant is obtained from the gNB, the transmitter UE may only transmit a single transport block (TB). As a result, this type of grant may be suitable for traffic with a loose latency requirement.

Configured grant: For traffic with a strict latency requirement, performing the four-message exchange procedure to request sidelink resources may induce unacceptable latency. In this case, prior to the traffic arrival, a transmitter UE may perform the four-message exchange procedure and request a set of resources. If a grant may be obtained from a gNB, then the requested resources may be reserved in a periodic manner. Upon arrival of traffic at a transmitter UE, this UE may launch the PSCCH and the PSSCH on the upcoming resource occasion. In fact, this type of grant is also known as grant-free transmissions.

In both dynamic grant and configured grant, a sidelink receiver UE cannot receive the DCI (since it is addressed to the transmitter UE), and therefore the receiver UE should perform blind decoding to identify presence of PSCCH and find resources for the PSSCH through the SCI. When the transmitter UE launches the PSCCH, CRC is also inserted in the SCI without any scrambling.

In the Mode 2 resource allocation, when traffic arrives at a transmitter UE, this transmitter UE should autonomously select resources for the PSCCH and the PSSCH. To further minimize latency of feedback HARQ ACK/NACK transmissions and subsequent retransmissions, the transmitter UE may also reserve resources for PSCCH/PSSCH for the retransmissions. To further enhance a probability of successful TB decoding at one shot and thus suppressing a probability to perform retransmissions, the transmitter UE may repeat the TB transmission along with the initial TB transmission. This mechanism is also known as blind retransmission. As a result, when traffic arrives at a transmitter UE, this transmitter UE should select resources for the following transmissions:

1) The PSSCH associated with the PSCCH for initial transmission and blind retransmissions.

2) The PSSCH associated with the PSCCH for retransmissions.

Since each transmitter UE in sidelink transmissions should autonomously select resources for above transmissions, how to prevent different transmitter UEs from selecting the same resources turns out to be a critical issue in Mode 2. A particular resource selection procedure is therefore imposed to Mode 2 based on channel sensing. The channel sensing algorithm involves measuring reference signal received power (RSRP) on different subchannels and requires knowledge of the different UEs' power levels of DMRS on the PSSCH or the DMRS on the PSCCH depending on the configuration. This information is known only after receiver SCI launched by (all) other UEs. The sensing and selection algorithm may be complex.

UE energy saving is an important performance indicator. There is no energy saving feature defined for SideLink until 3 GPP Rel-16. In the 3 GPP Rel-17 WI on NR sidelink enhancement, the following objective on UE Sidelink energy saving has been agreed and will be studied in 3GPP Rel-17 time frame. Sidelink discontinuous reception (DRX) for broadcast, groupcast, and unicast [RAN2]

1) defines on- and off-durations in sidelink and specifies the corresponding UE procedure;

2) specifies a mechanism aiming to align sidelink DRX wake-up time among the UEs communicating with each other;

3) specifies mechanism aiming to align sidelink DRX wake-up time with Uu DRX wake-up time in an in-coverage UE.

From the above objectives, DRX mechanisms for Sidelink may be designed and specified in 3GPP Rel-17.

As described in the third objective, SL DRX configuration needs to be aligned with Uu DRX configuration. In case of Mode 1 resource allocation, a UE gets SL grants from its serving gNB. However, in the case that the UE is configured with SL DRX and Uu DRX, a Scheduling Request (SR) would be triggered for requesting sidelink shared channel (SL-SCH) resources for new transmissions when triggered by the Sidelink BSR or the SL-CSI reporting. Per DRX rules regarding UE’s active time, the UE will be in active time for Uu DRX. The UE will keep in active time until the SR is cancelled. The grant will be cancelled when the UE has received sufficient grants (PUSCH grants and/or SL grants) and finished corresponding transmissions.

However, when the UE has received an SL grant towards a peer UE on an SL, the peer UE may be in DRX inactive state. This would lead to data loss on the SL.

Therefore, it may be important to design a mechanism to achieve alignment between the UE’s Uu active time and its peer UE’s SL active time.

A scenario comprising a first UE (UE1) served by a first cell (celll) may be provided. UE1 is further configured to communicate with at least one another UE, a second UE (UE2), on sidelink resources. UE1 and UE2 are capable of SL operations. Examples of SL operations are transmission of SL signals by UE1, reception of SL signals at UE1 from UE2, etc. To enable UL and SL operations, UE1 is further configured with one or more SL resources and one or more UL resources. At least one of the SL resources may be a SL time resource and also at least one of the UL resources may be a UL time resource. Examples of time resources are symbol, slot, subframe, frame, etc. The UE transmits UL signals on one or more UL resources to at least cell 1 , i.e., to the serving cell. The UE transmits and/or receives SL signals on one or more SL resources to at least UE2. Examples of the UL signals are SRS, DMRS, PUCCH, PUSCH, RACH, etc. Examples of the SL signals are DMRS, PSCCH, PSSCH, PSFCH, etc.

The term time resource used herein may correspond to any type of physical resource or radio resource expressed in terms of length of time. Examples of time resources are: symbol, time slot, subframe, radio frame, transmission time interval (TTI), interleaving time, etc. The term TTI used herein may correspond to any time period over which a physical channel may be encoded and optionally interleaved for transmission. The physical channel is decoded by the receiver over the same time period over which it was encoded. The TTI may also interchangeably called as short TTI (sTTI), transmission time, slot, sub-slot, mini-slot, mini-subframe, etc.

The term time- frequency resource used herein for any radio resource may be defined in any time-frequency resource grid in a cell. Examples of the time-frequency resource are subcarrier, resource block (RB), etc. The RB may also be interchangeably called as physical RB (PRB), virtual RB (VRB), etc.

A link or radio link over which the signals are transmitted between at least two UEs for device to device communication (D2D) operation is called herein as the sidelink (SL). The signals transmitted between the UEs for D2D operation are called herein as SL signals. The term SL may also interchangeably be called as D2D link, vehicle to everything (V2X) link, prose link, peer-to-peer link, PC5 link, etc. The SL signals may also interchangeably be called as V2X signals, D2D signals, prose signals, PC5 signals, peer-to-peer signals etc. The proposed mechanisms in the embodiments of the present disclosure are applicable to a first UE (UE1) with both UL and SL operations. UE1 connects to at least a second UE (UE2) via an SL. UE1 is configured with both Uu DRX and SL DRX. UE2 is configured with SL DRX. Uu DRX may be also configured. UE1 performs SL transmissions towards UE2 on the SL using SL grants obtained with resource allocation Mode 1, i.e., the SL grants are scheduled by the serving gNB of UE1.

In the embodiments of the present disclosure, the wording “at least one of’ is used in the description of signaling alternatives between two nodes (i.e., between two UEs, or between a gNB and a UE). This wording means that a node may transmit the signaling information to another node using one or more than one alternative. For the latter case, the node applies several different signaling alternatives to transmit the same content of the information to the other node to improve the transmission reliability.

In the first embodiment, the first UE (UE1) has pending transmissions towards its peer UE on an SL. For the peer UE (UE2) connected to the SL, UE1 informs its serving gNB of information that UE1 has pending SL transmissions towards UE2. Fig. 2 is a diagram illustrating a procedure for a gNB to inform UE2 that UE1 has the pending SL transmissions. When UEUs serving gNB has learned that UE1 has the pending SL transmissions towards UE2, the gNB may signal UE2 to prepare for incoming receptions from UE1 on the SL, so that UE2 will be in active time when UE1 starts transmissions on the SL to UE2 using the grants received from the gNB.

The gNB may learn that UE1 has the pending SL transmissions towards UE2 via at least one of the below signals from UE1.

• Alternative 1: UE1 has informed the gNB via at least an SR on PUCCH indicating that UE1 has the pending SL transmissions towards UE2.

UE1 may trigger an SR, so UE1 may become SR pending. The SR may be triggered due to one of the below events:

^• arrival of new SL transmissions on an SL;

^• trigger of SL CSI reporting. ^• Alternative 2: UE1 has informed the gNB via at least a BSR (e.g., SL BSR) on PUSCH indicating that UE1 has the pending SL transmissions towards UE2.

• Alternative 3: UE1 has informed the gNB via a RACH transmission indicating that UE1 has the pending SL transmissions towards UE2.

The RACH transmission may be an Msgl transmission in the case of 4-step RACH procedure or an MsgA transmission in the case of 2-step RACH procedure.

The RACH transmission may be an Msg3 transmission in the case of 4-step RACH procedure.

The RACH transmission may be an Msg5 transmission in the case of 4-step RACH procedure. The Msg5 may be an RRCSetupComplete message.

Dedicated physical RACH (PRACH) preambles or RACH occasions (ROs) may be allocated to UE1 to indicate that UE1 has the pending SL transmissions towards one or multiple specific peer UEs. The one or multiple peer UEs may include UE2.

An indicator indicating that UE1 has the pending SL transmissions towards UE2 may be included in the RACH transmission. The indicator may be carried in a MAC subheader, or a MAC CE, or an RRC message during the RACH transmission.

• Alternative 4: UE1 has informed the gNB via another UL transmission indicating that UE1 has the pending SL transmissions towards UE2.

The UL transmission may be a non-SR transmission on PUCCH (e.g., repurpose certain fields in a PUCCH transmission), or SRS transmission. Specific PUCCH resources or SRS resources may be allocated to UE1 to indicate that UE1 has the pending SL transmissions towards one or multiple specific peer UEs. The one or multiple peer UEs may include UE2.

In an example, UE1 may first send an SR to the gNB, and the gNB may assign a small grant; UE1 may then send a BSR to the gNB, and the gNB may assign a bigger grant.

The gNB may send a signaling to UE2 via at least one of the below signaling alternatives:

^• RRC signaling (such as Uu RRC),

^• MAC CE, and

^• layer 1, LI, signaling such as PDCCH.

In an example, the gNB may send DCI (e.g., DCI format 2-6) with CRC scrambled by PS-RNTI to UE2.

The gNB may use a wakeup signaling which has been standardized in NR Rel-16 to wake up UE2.

In an example, UE2 may first check if DCI (e.g., DCI format 2-6) with CRC scrambled by PS-RNTI has been detected outside active time. In the affirmative, UE2 may wake up. Otherwise, UE2 may further check if an RRC parameter “ps-WakeUp” has been configured with a value “true”, and if so, UE2 may wake up; if not, UE2 may not wake up.

In the second embodiment, the first UE (UE1) has pending transmissions towards its peer UE on an SL. For the peer UE (UE2) connected to the SL, while UE1 informs its serving gNB of the information that UE1 has the pending SL transmissions towards UE2, UE1 also informs UE2 of the information. Fig. 3 is a diagram illustrating a procedure for UE1 to inform UE2 that UE1 has the pending SL transmissions. UE2 may thereafter prepare for incoming receptions from UE1 on the SL, so that UE2 will be in active time when UE1 starts transmissions on the SL to UE2 using the grant received from the gNB.

UE1 informs UE2 that UE1 has the pending SL transmissions towards UE2 via at least one of the below alternatives.

Alternative 1: PC5-RRC signaling;

Alternative 2: MAC CE;

Alternative 3: control PDU (protocol data unit) of a protocol layer such as SDAP (service data adaptation protocol), PDCP (packet data convergence protocol), RLC (radio link control) or an adaptation layer in case of SL relay; Alternative 4: LI signaling, e.g., which includes at least one of: o LI signaling on PSCCH or PSSCH, a new SCI format may be introduced accordingly. Alternatively, reuse fields in an existing SCI format. Single or multiple bits may be occupied for the signaling. o LI signaling on PSFCH. Single or multiple bits may be occupied for the signaling. o A new physical channel may be designed for the signaling. Single or multiple bits may be occupied for the signaling.

For the first three alternatives, UE1 may use any SL grant to transmit the signaling, e.g., any of previous SL grants. Alternatively, UE1 may be allocated with specific configured grants on the SL to transfer the signaling to UE2.

UE2 may be configured with periodic occasions in time for reception of the signaling. UE2 will be active during these occasions regardless of whether its SL DRX state is active or inactive. Alternatively, UE2 will be only active during the occasions which are overlapped with the DRX active time.

In the third embodiment, as described above in the first or second embodiment, the signaling sent to UE2 about the information that UE1 has the pending SL transmissions towards UE2 may comprise at least one of the below information elements: The types of the pending transmissions such as PSSCH, PSCCH, PSFCH, SL-PSS, or SL-SSS, etc;

• The traffic types, service types, application types, priority indicators, logical channels (LCHs), or logical channel groups (LCGs) which are associated with the pending transmissions;

• The time when the pending transmissions are expected to start;

• The time duration that the pending transmissions are expected to last;

• The data volume which are associated with the pending transmissions.

In the fourth embodiment, in the case that UE1 and UE2 are being served by different gNBs, in order to inform UE2 that UE1 has the pending SL transmissions towards UE2, UEl’s serving gNB (gNBl) may send a signaling to UE2’s serving gNB (gNB2) via inter- gNB signaling. Fig. 4 is a diagram illustrating a procedure for a gNB (gNBl) to inform a UE (UE2) via inter-gNB signaling indicating that a UE it serves (UE1) has the pending SL transmissions to the peer gNB(gNB2)’s serving UE (UE2). After that, gNB2 may send the signaling to UE2 via the signaling alternatives as described in the first embodiment.

The signaling transmitted by gNBl to gNB2 and then to UE2 may include two separate signalings, i.e., a signaling from gNBl to gNB2 and a signaling from gNB2 to UE2, and both signalings have the same content.

In the fifth embodiment, for any one of the above embodiments, upon reception of the signaling from UE1, UE2 may be aware that UE1 has the pending transmission on the SL. UE2 may choose one of the below options to adjust its active time:

Option 1 : goes to an active state immediately upon reception of the signaling;

Option 2: goes to an active state at an expected time if the signaling carries that information;

Option 3: goes to an active state at an estimated time upon reception of the signaling. In this option, a time when to go to the active state would depend on UE2’s estimation. UE2 may estimate how soon UE1 will start the transmissions on the SL. The estimation may be performed by UE2 considering knowledge of a resource congestion level on concerned resource pools. The congestion level may be determined in terms of such as channel busy ratio (CBR) or channel usage ratio (CR), or HARQ NACK ratio. Generally speaking, UE2 may wait for a longer time to go to the active state if the estimated/measured congestion ratio is higher; otherwise, UE2 may wait for a shorter time to go to the active state if the estimated/measured congestion ratio is lower.

For any one of the above options, as soon as UE2 goes to an active state, UE2 may start a timer, and the timer expiration time may be set according to the received information in the signaling (e.g., the time duration that the transmissions are expected to last). After the timer is expired, UE2 goes to a sleep state. Alternatively, UE2 may go to the sleep state upon reception of a signaling indicating that UE2 shall go to the sleep state. The signaling may be received from a gNB or from UE1.

In the sixth embodiment, for any one of the above embodiments, the concerned configuration (e.g., which option or alternative should be applied) of the UE (i.e., UE1 or UE2) is signaled by a network node (such as gNB) or a controlling UE. In addition, the configuration may be pre-configured to the UE especially when the UE is out of coverage.

In the seventh embodiment, for the above embodiments (e.g., the first, second and fourth embodiments), the gNB’s functionalities may be performed by a controlling UE. In a more general case, the gNB performs configuration to UE1, while a controlling UE assigns an SL grant to UE1; alternatively, the gNB assigns an SL grant to UE1, while the controlling UE performs configuration to UE1.

Fig. 5 is a flow chart illustrating a method 500 implemented on a first terminal device according to some embodiments of the present disclosure. As an example, operations of this flow chart may be performed by a first UE which may act as UE1 as illustrated in Figs. 2-4, but they are not limited thereto. The operations in this and other flow charts will be described with reference to the exemplary embodiments of the other figures. However, it should be appreciated that the operations of the flow charts may be performed by embodiments of the present disclosure other than those discussed with reference to the other figures, and the embodiments of the present disclosure discussed with reference to these other figures may perform operations different than those discussed with reference to the flow charts.

In one embodiment, the first UE may transmit, to a control node, a first signaling indicating that the first UE has pending transmissions on a sidelink towards a second UE (block 501). By way of example, the second UE may act as UE2 shown in Figs. 2-4. The first UE may receive a sidelink grant from the control node (block 502). Then, the first UE may initiate transmissions on the sidelink to the second UE based on the sidelink grant (block 503).

As an example, the first signaling may be transmitted via at least one of: an SR on a PUCCH; a buffer status report on a PUSCH; a RACH transmission; a non-SR transmission on the PUCCH; and an SRS transmission.

As a further example, the scheduling request may be triggered by at least one of: arrival of new sidelink transmissions on the sidelink; and trigger of sidelink CSI reporting.

As a further example, the RACH transmission may be one of the following: an Msgl transmission in the case of 4-step RACH procedure; an MsgA transmission in the case of 2-step RACH procedure; an Msg3 transmission in the case of 4-step RACH procedure; and an Msg5 transmission in the case of 4-step RACH procedure.

As a further example, in the case that the first signaling is transmitted via the RACH transmission, dedicated PRACH or RACH occasions may be allocated to the first UE to indicate that the first UE has pending sidelink transmissions towards one or more UEs.

As a further example, an indicator indicating that the first UE has the pending transmissions on the sidelink towards the second UE and included in the RACH transmission may be carried in a MAC subheader, or in a MAC CE, or in an RRC message during the RACH transmission.

As a further example, in the case that the first signaling is transmitted via the SR or the non-SR transmission on the PUCCH and/or the SRS transmission, PUCCH resources and/or SRS resources may be allocated to the first UE to indicate that the first UE has pending sidelink transmissions towards one or more UEs.

As an example, the method 500 may further comprise: transmitting, to the second UE, a second signaling indicating that the first UE has the pending sidelink transmissions towards the second UE. As a further example, the second signaling may be at least one of: PC5-RRC signaling; MAC CE; a control PDU of a protocol layer; and LI signaling.

As a further example, in the case that the second signaling is at least one of the PC5-RRC signaling, the MAC CE and the control PDU, configured sidelink grants may be allocated to the first UE to transmit the second signaling.

As a further example, the LI signaling may include at least one of: LI signaling on a PSCCH; and LI signaling on a PSSCH.

As a further example, the second signaling may comprise at least of: types of the pending transmissions; traffic types, service types, application types, priority indicators, logical channels or logical channel groups associated with the pending transmissions; time when the pending transmissions are expected to start; duration in which the pending transmissions are expected to last; and a data volume associated with the pending transmissions.

As an example, configurations of the first UE and the second UE may be signaled by the control node or preconfigured.

As an example, the control node may be a gNB, or a controlling UE, or a combination of the gNB and the controlling UE.

Fig. 6 is a flow chart illustrating a method 600 implemented on a control node according to some embodiments of the present disclosure. As an example, operations of this flow chart may be performed by the gNB as illustrated in Figs 2 and 3 or gNBl as illustrated in Fig. 4 or a controlling UE.

In one embodiment, the control node may receive, from a first UE, a first signaling indicating that the first UE has pending transmissions on a sidelink towards a second UE (block 601). By way of example, the first UE and the second UE may act as UE1 and UE2 shown in Figs. 2-4 respectively. The control node may transmit a sidelink grant to the first UE (block 602). As an example, the first signaling may be received via at least one of: an SR on a PUCCH; a buffer status report on a PUSCH; a RACH transmission; a non-SR transmission on the PUCCH; and an SRS transmission.

As a further example, the method 600 may further comprise: in the case that the first signaling is received via the RACH transmission, allocating dedicated PRACH or RACH occasions to indicate that the first UE has pending sidelink transmissions towards one or more UE.

As a further example, the method 600 may further comprise: in the case that the first signaling is received via the SR or the non-SR transmission on the PUCCH and/or the SRS transmission, allocating PUCCH resources and/or SRS resources to indicate that the first UE has pending sidelink transmissions towards one or more UEs.

As an example, the method 600 may further comprise: transmitting, to the second UE, a signaling indicating that the first UE has the pending sidelink transmissions towards the second UE.

As a further example, the signaling may be transmitted to the second UE via at least one of: RRC signaling; MAC CE; and LI signaling.

As a further example, the signaling transmitted to the second UE may be used by the control node to wake up the second UE.

As a further example, the signaling transmitted to the second UE may comprise at least of: types of the pending transmissions; traffic types, service types, application types, priority indicators, logical channels or logical channel groups associated with the pending transmissions; time when the pending transmissions are expected to start; duration in which the pending transmissions are expected to last; and a data volume associated with the pending transmissions.

As a further example, the signaling may be transmitted by way of a serving control node for the second UE.

Fig. 7 is a flow chart illustrating a method 700 implemented on a second terminal device according to some embodiments of the present disclosure. As an example, operations of this flow chart may be performed by a second UE which may act as UE2 as illustrated in Figs. 2-4.

In one embodiment, the second UE may receive a signaling indicating that a first UE has pending transmissions on a sidelink towards the second UE (block 701). By way of example, the first UE may act as UE1 shown in Figs. 2-4. The second UE may enter an active state (block 702) and then receive transmissions on the sidelink from the first UE (block 703).

As an example, the signaling may be received from a control node.

As a further example, the signaling may be at least one of: RRC signaling; MAC CE; and LI signaling.

As a further example, the signaling may be used by the control node to wake up the second UE.

As a further example, the signaling may be received from the first UE.

As a further example, the signaling may be at least one of: PC5-RRC signaling; MAC CE; a control PDU of a protocol layer; and LI signaling.

As a further example, the second UE may be configured with periodic occasions in time for reception of the signaling, regardless of whether a sidelink discontinuous reception state of the second UE is active. As a further example, the second UE may be active only during occasions which are overlapped with a discontinuos reception active time.

As an example, the signaling may comprise at least of: types of the pending transmissions; traffic types, service types, application types, priority indicators, logical channels or logical channel groups associated with the pending transmissions; time when the pending transmissions are expected to start; duration in which the pending transmissions are expected to last; and a data volume associated with the pending transmissions.

As an example, the second UE may enter the active state in one of the following modes: immediately upon reception of the signaling; at an expected time indicated by the signaling; and at an estimated time from reception of the signaling.

As a further example, the estimated time may be determined by the second UE based on a resource congestion level on resource pools.

As a further example, the resource congestion level may be determined based on a channel busy ratio, or a channel usage ratio, or a HARQ NACK ratio.

As an example, configurations of the first UE and the second UE may be signaled by a control node or preconfigured.

As a further example, the control node may be a gNB, or a controlling UE, or a combination of the gNB and the controlling UE.

Fig. 8 is a block diagram illustrating a first terminal device 800 according to some embodiments of the present disclosure. As an example, the first terminal device 800 may act as UE1 as illustrated in Figs. 2-4, but it is not limited thereto. It should be appreciated that the first terminal device 800 may be implemented using components other than those illustrated in Fig. 8.

With reference to Fig. 8, the first terminal device 800 may comprise at least a processor 801, a memory 802, a network interface 803 and a communication medium 804. The processor 801, the memory 802 and the network interface 803 may be communicatively coupled to each other via the communication medium 804. The processor 801 may include one or more processing units. A processing unit may be a physical device or article of manufacture comprising one or more integrated circuits that read data and instructions from computer readable media, such as the memory 802, and selectively execute the instructions. In various embodiments, the processor 801 may be implemented in various ways. As an example, the processor 801 may be implemented as one or more processing cores. As another example, the processor 801 may comprise one or more separate microprocessors. In yet another example, the processor 801 may comprise an application-specific integrated circuit (ASIC) that provides specific functionality. In still another example, the processor 801 may provide specific functionality by using an ASIC and/or by executing computer-executable instructions.

The memory 802 may include one or more computer-usable or computer-readable storage medium capable of storing data and/or computer-executable instructions. It should be appreciated that the storage medium is preferably a non-transitory storage medium.

The network interface 803 may be a device or article of manufacture that enables the first terminal device 800 to send data to or receive data from other devices. In different embodiments, the network interface 803 may be implemented in different ways. As an example, the network interface 803 may be implemented as an Ethernet interface, a token-ring network interface, a fiber optic network interface, a network interface (e.g., Wi-Fi, WiMax, etc.), or another type of network interface.

The communication medium 804 may facilitate communication among the processor 801, the memory 802 and the network interface 803. The communication medium 804 may be implemented in various ways. For example, the communication medium 804 may comprise a Peripheral Component Interconnect (PCI) bus, a PCI Express bus, an accelerated graphics port (AGP) bus, a serial Advanced Technology Attachment (ATA) interconnect, a parallel ATA interconnect, a Fiber Channel interconnect, a USB bus, a Small Computing System Interface (SCSI) interface, or another type of communications medium. In the example of Fig. 8, the instructions stored in the memory 802 may include those that, when executed by the processor 801, cause the first terminal device 800 to implement the method described with respect to Fig. 5.

Fig. 9 is another block diagram illustrating a first terminal device 900 according to some embodiments of the present disclosure. As an example, the first terminal device 900 may act as UE1 as illustrated in Figs. 2-4, but it is not limited thereto. It should be appreciated that the first terminal device 900 may be implemented using components other than those illustrated in Fig. 9.

With reference to Fig. 9, the first terminal device 900 may comprise at least a transmission unit 901, a receiving unit 902 and an initiation unit 903. The transmission unit 901 may be adapted to perform at least the operation described in the block 501 of Fig. 5. The receiving unit 902 may be adapted to perform at least the operation described in the block 502 of Fig. 5. The initiation unit 903 may be adapted to perform at least the operation described in the block 503 of Fig. 5.

Fig. 10 is a block diagram illustrating a control node 1000 according to some embodiments of the present disclosure. As an example, the control node 1000 may act as the gNB as illustrated in Figs. 2 and 3 or gNBl as illustrated in Fig. 4 or a controlling UE. It should be appreciated that the control node 1000 may be implemented using components other than those illustrated in Fig. 10.

With reference to Fig. 10, the control node 1000 may comprise at least a processor 1001, a memory 1002, a network interface 1003 and a communication medium 1004. The processor 1001, the memory 1002 and the network interface 1003 are communicatively coupled to each other via the communication medium 1004.

The processor 1001, the memory 1002, the network interface 1003 and the communication medium 1004 are structurally similar to the processor 801, the memory 802, the network interface 803 and the communication medium 804 respectively, and will not be described herein in detail.

In the example of Fig. 10, the instructions stored in the memory 1002 may include those that, when executed by the processor 1001, cause the control node 1000 to implement the method described with respect to Fig. 6.

Fig. 11 is another block diagram illustrating a control node 1100 according to some embodiments of the present disclosure. As an example, the control node 1100 may act as the gNB as illustrated in Figs. 2 and 3 or gNBl as illustrated in Fig. 4 or a controlling UE. It should be appreciated that the control node 1100 may be implemented using components other than those illustrated in Fig. 11.

With reference to Fig. 11 , the control node 1100 may comprise at least a receiving unit 1101 and a transmission unit 1102. The receiving unit 1101 may be adapted to perform at least the operation described in the block 601 of Fig. 6. The transmission unit 1102 may be adapted to perform at least the operation described in the block 602 of Fig. 6.

Fig. 12 is a block diagram illustrating a second terminal device 1200 according to some embodiments of the present disclosure. As an example, the second terminal device 1200 may act as UE2 as illustrated in Figs. 2-4. It should be appreciated that the second terminal device 1200 may be implemented using components other than those illustrated in Fig. 12.

With reference to Fig. 12, the second terminal device 1200 may comprise at least a processor 1201, a memory 1202, a network interface 1203 and a communication medium 1204. The processor 1201, the memory 1202 and the network interface 1203 are communicatively coupled to each other via the communication medium 1204.

The processor 1201, the memory 1202, the network interface 1203 and the communication medium 1204 are structurally similar to the processor 801 or 1001, the memory 802 or 1002, the network interface 803 or 1003 and the communication medium 804 or 1004 respectively, and will not be described herein in detail.

In the example of Fig. 12, the instructions stored in the memory 1202 may include those that, when executed by the processor 1201, cause second terminal device 1200 to implement the method described with respect to Fig. 7.

Fig. 13 is another block diagram illustrating a second terminal device 1300 according to some embodiments of the present disclosure. As an example, the second terminal device 1300 may act as UE2 as illustrated in Figs. 2-4. It should be appreciated that the second terminal device 1300 may be implemented using components other than those illustrated in Fig. 13.

With reference to Fig. 13, the second terminal device 1300 may comprise at least a receiving unit 1301 and an entering unit 1302. The receiving unit 1301 may be adapted to perform at least the operations described in the blocks 701 and 703 of Fig. 7. The entering unit 1302 may be adapted to perform at least the operation described in the block 702 of Fig. 7.

The units shown in Figs. 9, 11 and 13 may constitute machine-executable instructions embodied within a machine, e.g., readable medium, which when executed by a machine will cause the machine to perform the operations described. Besides, any of these units may be implemented as hardware, such as an application specific integrated circuit (ASIC), Digital Signal Processor (DSP), Field Programmable Gate Array (FPGA) or the like.

Moreover, it should be appreciated that the arrangements described herein are set forth only as examples. Other arrangements (e.g., more controllers or more detectors, etc.) may be used in addition to or instead of those shown, and some units may be omitted altogether. Functionality and cooperation of these units are correspondingly described in more detail with reference to Figs. 5-7.

Fig. 14 is a block diagram illustrating a wireless communication system 1400 according to some embodiments of the present disclosure. The wireless communication system 1400 comprises at least a first terminal device 1401, a control node 1402 and a second terminal device 1403. In one embodiment, the first terminal device 1401 may act as the first terminal device 800 or 900 as depicted in Fig. 8 or 9, the control node 1402 may act as the control node 1000 or 1100 as depicted in Fig. 10 or 11, and the second terminal device 1403 may act as the second terminal device 1200 or 1300 as depicted in Fig. 12 or 13. In one embodiment, the first terminal device 1401, the control node 1402 and the second terminal device 1403 may communicate with each other.

Fig. 15 is a block diagram schematically illustrating a telecommunication network connected via an intermediate network to a host computer.

With reference to Fig. 15, in accordance with an embodiment, a communication system includes a telecommunication network 1510, such as a 3GPP-type cellular network, which comprises an access network 1511, such as a radio access network, and a core network 1514. The access network 1511 comprises a plurality of base stations 1512a, 1512b, 1512c, such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 1513a, 1513b, 1513c. Each base station 1512a, 1512b, 1512c is connectable to the core network 1514 over a wired or wireless connection 1515. A first user equipment (UE) 1591 located in coverage area 1513c is configured to wirelessly connect to, or be paged by, the corresponding base station 1512c. A second UE 1592 in coverage area 1513a is wirelessly connectable to the corresponding base station 1512a. While a plurality of UEs 1591, 1592 are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station 1512.

The telecommunication network 1510 is itself connected to a host computer 1530, which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server or as processing resources in a server farm. The host computer 1530 may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. The connections 1521, 1522 between the telecommunication network 1510 and the host computer 1530 may extend directly from the core network 1514 to the host computer 1530 or may go via an optional intermediate network 1520. The intermediate network 1520 may be one of, or a combination of more than one of, a public, private or hosted network; the intermediate network 1520, if any, may be a backbone network or the Internet; in particular, the intermediate network 1520 may comprise two or more sub-networks (not shown).

The communication system of Fig. 15 as a whole enables connectivity between one of the connected UEs 1591, 1592 and the host computer 1530. The connectivity may be described as an over-the-top (OTT) connection 1550. The host computer 1530 and the connected UEs 1591, 1592 are configured to communicate data and/or signaling via the OTT connection 1550, using the access network 1511, the core network 1514, any intermediate network 1520 and possible further infrastructure (not shown) as intermediaries. The OTT connection 1550 may be transparent in the sense that the participating communication devices through which the OTT connection 1550 passes are unaware of routing of uplink and downlink communications. For example, a base station 1512 may not or need not be informed about the past routing of an incoming downlink communication with data originating from a host computer 1530 to be forwarded (e.g., handed over) to a connected UE 1591. Similarly, the base station 1512 need not be aware of the future routing of an outgoing uplink communication originating from the UE 1591 towards the host computer 1530.

Example implementations, in accordance with an embodiment, of the UE, base station and host computer discussed in the preceding paragraphs will now be described with reference to Fig. 16. In a communication system 1600, a host computer 1610 comprises hardware 1615 including a communication interface 1616 configured to set up and maintain a wired or wireless connection with an interface of a different communication device of the communication system 1600. The host computer 1610 further comprises processing circuitry 1618, which may have storage and/or processing capabilities. In particular, the processing circuitry 1618 may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The host computer 1610 further comprises software 1611, which is stored in or accessible by the host computer 1610 and executable by the processing circuitry 1618. The software 1611 includes a host application 1612. The host application 1612 may be operable to provide a service to a remote user, such as a UE 1630 connecting via an OTT connection 1650 terminating at the UE 1630 and the host computer 1610. In providing the service to the remote user, the host application 1612 may provide user data which is transmitted using the OTT connection 1650.

The communication system 1600 further includes a base station 1620 provided in a telecommunication system and comprising hardware 1625 enabling it to communicate with the host computer 1610 and with the UE 1630. The hardware 1625 may include a communication interface 1626 for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system 1600, as well as a radio interface 1627 for setting up and maintaining at least a wireless connection 1670 with a UE 1630 located in a coverage area (not shown in Fig. 16) served by the base station 1620. The communication interface 1626 may be configured to facilitate a connection 1660 to the host computer 1610. The connection 1660 may be direct or it may pass through a core network (not shown in Fig. 16) of the telecommunication system and/or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, the hardware 1625 of the base station 1620 further includes processing circuitry 1628, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The base station 1620 further has software 1621 stored internally or accessible via an external connection.

The communication system 1600 further includes the UE 1630 already referred to. Its hardware 1635 may include a radio interface 1637 configured to set up and maintain a wireless connection 1670 with a base station serving a coverage area in which the UE 1630 is currently located. The hardware 1635 of the UE 1630 further includes processing circuitry 1638, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The UE

1630 further comprises software 1631, which is stored in or accessible by the UE 1630 and executable by the processing circuitry 1638. The software

1631 includes a client application 1632. The client application 1632 may be operable to provide a service to a human or non-human user via the UE 1630, with the support of the host computer 1610. In the host computer 1610, an executing host application 1612 may communicate with the executing client application 1632 via the OTT connection 1650 terminating at the UE 1630 and the host computer 1610. In providing the service to the user, the client application 1632 may receive request data from the host application 1612 and provide user data in response to the request data. The OTT connection 1650 may transfer both the request data and the user data. The client application 1632 may interact with the user to generate the user data that it provides.

It is noted that the host computer 1610, base station 1620 and UE 1630 illustrated in Fig. 16 may be identical to the host computer 1530, one of the base stations 1512a, 1512b, 1512c and one of the UEs 1591, 1592 of Fig. 15, respectively. This is to say, the inner workings of these entities may be as shown in Fig. 16 and independently, the surrounding network topology may be that of Fig. 15.

In Fig. 16, the OTT connection 1650 has been drawn abstractly to illustrate the communication between the host computer 1610 and the use equipment 1630 via the base station 1620, without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from the UE 1630 or from the service provider operating the host computer 1610, or both. While the OTT connection 1650 is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network).

The wireless connection 1670 between the UE 1630 and the base station 1620 is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to the UE 1630 using the OTT connection 1650, in which the wireless connection 1670 forms the last segment. More precisely, the teachings of these embodiments may improve the radio resource utilization and thereby provide benefits such as reduced user waiting time.

A measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection 1650 between the host computer 1610 and UE 1630, in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection 1650 may be implemented in the software 1611 of the host computer 1610 or in the software 1631 of the UE 1630, or both. In embodiments, sensors (not shown) may be deployed in or in association with communication devices through which the OTT connection 1650 passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software 1611, 1631 may compute or estimate the monitored quantities. The reconfiguring of the OTT connection 1650 may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect the base station 1620, and it may be unknown or imperceptible to the base station 1620. Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling facilitating the host computer’s 1610 measurements of throughput, propagation times, latency and the like. The measurements may be implemented in that the software 1611, 1631 causes messages to be transmitted, in particular empty or ‘dummy’ messages, using the OTT connection 1650 while it monitors propagation times, errors etc.

Fig. 17 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Figs. 15 and 16. For simplicity of the present disclosure, only drawing references to Fig. 17 will be included in this section. In a first step 1710 of the method, the host computer provides user data. In an optional substep 1711 of the first step 1710, the host computer provides the user data by executing a host application. In a second step 1720, the host computer initiates a transmission carrying the user data to the UE. In an optional third step 1730, the base station transmits to the UE the user data which was carried in the transmission that the host computer initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In an optional fourth step 1740, the UE executes a client application associated with the host application executed by the host computer.

Fig. 18 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Fig. 15 and 16. For simplicity of the present disclosure, only drawing references to Fig. 18 will be included in this section. In a first step 1810 of the method, the host computer provides user data. In an optional substep (not shown) the host computer provides the user data by executing a host application. In a second step 1820, the host computer initiates a transmission carrying the user data to the UE. The transmission may pass via the base station, in accordance with the teachings of the embodiments described throughout this disclosure. In an optional third step 1830, the UE receives the user data carried in the transmission.

Fig. 19 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Figs. 15 and 16. For simplicity of the present disclosure, only drawing references to Fig. 19 will be included in this section. In an optional first step 1910 of the method, the UE receives input data provided by the host computer. Additionally or alternatively, in an optional second step 1920, the UE provides user data. In an optional substep 1921 of the second step 1920, the UE provides the user data by executing a client application. In a further optional substep 1911 of the first step 1910, the UE executes a client application which provides the user data in reaction to the received input data provided by the host computer. In providing the user data, the executed client application may further consider user input received from the user. Regardless of the specific manner in which the user data was provided, the UE initiates, in an optional third substep 1930, transmission of the user data to the host computer. In a fourth step 1940 of the method, the host computer receives the user data transmitted from the UE, in accordance with the teachings of the embodiments described throughout this disclosure.

Fig. 20 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Figs. 15 and 16. For simplicity of the present disclosure, only drawing references to Fig. 20 will be included in this section. In an optional first step 2010 of the method, in accordance with the teachings of the embodiments described throughout this disclosure, the base station receives user data from the UE. In an optional second step 2020, the base station initiates transmission of the received user data to the host computer. In a third step 2030, the host computer receives the user data carried in the transmission initiated by the base station.

Some portions of the foregoing detailed description have been presented in terms of algorithms and symbolic representations of transactions on data bits within a computer memory. These algorithmic descriptions and representations are ways used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of transactions leading to a desired result. The transactions are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.

It should be appreciated, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the above discussion, it is appreciated that throughout the description, discussions utilizing terms such as "processing" or "computing" or "calculating" or "determining" or "displaying" or the like, refer to actions and processes of a computer system, or a similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct more specialized apparatus to perform the required method transactions. The required structure for a variety of these systems will appear from the description above. In addition, embodiments of the present disclosure are not described with reference to any particular programming language. It should be appreciated that a variety of programming languages may be used to implement the teachings of embodiments of the present disclosure as described herein.

An embodiment of the present disclosure may be an article of manufacture in which a non-transitory machine-readable medium (such as microelectronic memory) has stored thereon instructions (e.g., computer code) which program one or more data processing components (generically referred to here as a “processor”) to perform the operations described above. In other embodiments, some of these operations might be performed by specific hardware components that contain hardwired logic (e.g., dedicated digital filter blocks and state machines). Those operations might alternatively be performed by any combination of programmed data processing components and fixed hardwired circuit components.

In the foregoing detailed description, embodiments of the present disclosure have been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the spirit and scope of the present disclosure as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

Throughout the description, some embodiments of the present disclosure have been presented through flow diagrams. It should be appreciated that the order of transactions and transactions described in these flow diagrams are only intended for illustrative purposes and not intended as a limitation of the present disclosure. One having ordinary skill in the art would recognize that variations can be made to the flow diagrams without departing from the spirit and scope of the present disclosure as set forth in the following claims.

Advantageous examples of the present disclosure can be phrased as follows: 1. A method (500) implemented by a first terminal device, the method comprising: transmitting (501), to a control node, a first signaling indicating that the first terminal device has pending transmissions on a sidelink towards a second terminal device; receiving (502) a sidelink grant from the control node; and initiating (503) transmissions on the sidelink to the second terminal device based on the sidelink grant.

2. The method of example 1, wherein the first signaling is transmitted via at least one of: a scheduling request, SR, on a physical uplink control channel, PUCCH; a buffer status report on a physical uplink shared channel, PUSCH; a random access channel, RACH, transmission; a non-SR transmission on the PUCCH; and a sounding reference signal, SRS, transmission.

3. The method of example 2, wherein the scheduling request is triggered by at least one of: arrival of new sidelink transmissions on the sidelink; and trigger of sidelink channel state information, CSI, reporting.

4. The method of example 2 or 3, wherein the RACH transmission is one of the following: an Msgl transmission in the case of 4-step RACH procedure; an MsgA transmission in the case of 2-step RACH procedure; an Msg3 transmission in the case of 4-step RACH procedure; and an Msg5 transmission in the case of 4-step RACH procedure. 5. The method of any of examples 2-4, wherein in the case that the first signaling is transmitted via the RACH transmission, dedicated physical random access channel, PRACH, or RACH occasions are allocated to the first terminal device to indicate that the first terminal device has pending sidelink transmissions towards one or more terminal devices.

6. The method of any of examples 2-5, wherein an indicator indicating that the first terminal device has the pending transmissions on the sidelink towards the second terminal device and included in the RACH transmission is carried in a media access control, MAC, subheader, or in a MAC control element, CE, or in a radio resource control, RRC, message during the RACH transmission.

7. The method of any of examples 2-6, wherein in the case that the first signaling is transmitted via the SR or the non- SR transmission on the PUCCH and/or the SRS transmission, PUCCH resources and/or SRS resources are allocated to the first terminal device to indicate that the first terminal device has pending sidelink transmissions towards one or more terminal devices.

8. The method of any of examples 1-7, further comprising: transmitting, to the second terminal device, a second signaling indicating that the first terminal device has the pending sidelink transmissions towards the second terminal device.

9. The method of example 8, wherein the second signaling is at least one of:

PC5-RRC signaling;

MAC CE; a control protocol data unit, PDU, of a protocol layer; and layer 1, LI, signaling. 10. The method of example 9, wherein in the case that the second signaling is at least one of the PC5-RRC signaling, the MAC CE and the control PDU, configured sidelink grants are allocated to the first terminal device to transmit the second signaling.

11. The method of example 9 or 10, wherein the LI signaling includes at least one of:

LI signaling on a physical sidelink control channel, PSCCH; and

LI signaling on a physical sidelink shared channel, PSSCH.

12. The method of any of examples 8-11, wherein the second signaling comprises at least of: types of the pending transmissions; traffic types, service types, application types, priority indicators, logical channels or logical channel groups associated with the pending transmissions; time when the pending transmissions are expected to start; duration in which the pending transmissions are expected to last; and a data volume associated with the pending transmissions.

13. The method of any of examples 1-12, wherein configurations of the first terminal device and the second terminal device are signaled by the control node or preconfigured.

14. The method of any of examples 1-13, wherein the control node is a gNB, or a controlling terminal device, or a combination of the gNB and the controlling terminal device.

15. A method (600) implemented by a control node, the method comprising: receiving (601), from a first terminal device, a first signaling indicating that the first terminal device has pending transmissions on a sidelink towards a second terminal device; and transmitting (602) a sidelink grant to the first terminal device.

16. The method of example 15, wherein the first signaling is received via at least one of: a scheduling request, SR, on a physical uplink control channel, PUCCH; a buffer status report on a physical uplink shared channel, PUSCH; a random access channel, RACH, transmission; a non-SR transmission on the PUCCH; and a sounding reference signal, SRS, transmission.

17. The method of example 16, wherein the RACH transmission is one of the following: an Msgl transmission in the case of 4-step RACH procedure; an MsgA transmission in the case of 2-step RACH procedure; an Msg3 transmission in the case of 4-step RACH procedure; and an Msg5 transmission in the case of 4-step RACH procedure.

18. The method of example 16 or 17, further comprising: in the case that the first signaling is received via the RACH transmission, allocating dedicated physical random access channel, PRACH, or RACH occasions to indicate that the first terminal device has pending sidelink transmissions towards one or more terminal devices.

19. The method of any of examples 16-18, wherein an indicator indicating that the first terminal device has the pending transmissions on the sidelink towards the second terminal device and included in the RACH transmission is carried in a media access control, MAC subheader, or in a MAC control element, CE, or in a radio resource control, RRC, message during the RACH transmission.

20. The method of any of examples 16-19, further comprising: in the case that the first signaling is received via the SR or the non-SR transmission on the PUCCH and/or the SRS transmission, allocating PUCCH resources and/or SRS resources to indicate that the first terminal device has pending sidelink transmissions towards one or more terminal devices.

21. The method of any of examples 15-20, further comprising: transmitting, to the second terminal device, a signaling indicating that the first terminal device has the pending sidelink transmissions towards the second terminal device.

22. The method of example 21, wherein the signaling is transmitted to the second terminal device via at least one of:

RRC signaling;

MAC CE; and layer 1, LI, signaling.

23. The method of examples 21 or 22, wherein the signaling transmitted to the second terminal device is used by the control node to wake up the second terminal device.

24. The method of any of examples 21-23, wherein the signaling transmitted to the second terminal device comprises at least of: types of the pending transmissions; traffic types, service types, application types, priority indicators, logical channels or logical channel groups associated with the pending transmissions; time when the pending transmissions are expected to start; duration in which the pending transmissions are expected to last; and a data volume associated with the pending transmissions.

25. The method of any of examples 21-24, wherein the signaling is transmitted by way of a serving control node for the second terminal device.

26. The method of any of examples 15-25, wherein configurations of the first terminal device and the second terminal device are signaled by the control node or preconfigured.

27. The method of any of examples 15-26, wherein the control node is a gNB, or a controlling terminal device, or a combination of the gNB and the controlling terminal device.

28. A method (700) implemented by a second terminal device, the method comprising: receiving (701) a signaling indicating that a first terminal device has pending transmissions on a sidelink towards the second terminal device; entering (702) an active state; and receiving (703) transmissions on the sidelink from the first terminal device.

29. The method of example 28, wherein the signaling is received from a control node.

30. The method of example 29, wherein the signaling is at least one of: radio resource control, RRC, signaling; media access control, MAC, control element, CE; and layer 1, LI, signaling. 31. The method of example 29 or 30, wherein the signaling is used by the control node to wake up the second terminal device.

32. The method of example 28, wherein the signaling is received from the first terminal device.

33. The method of example 32, wherein the signaling is at least one of:

PC5-RRC signaling;

MAC CE; a control protocol data unit, PDU, of a protocol layer; and

LI signaling.

34. The method of example 33, wherein the LI signaling includes at least one of:

LI signaling on a physical sidelink control channel, PSCCH; and

LI signaling on a physical sidelink shared channel, PSSCH.

35. The method of any of examples 32-34, wherein the second terminal device is configured with periodic occasions in time for reception of the signaling, regardless of whether a sidelink discontinuous reception state of the second terminal device is active.

36. The method of any of examples 32-34, wherein the second terminal device is active only during occasions which are overlapped with a discontinuos reception active time.

37. The method of any of examples 28-36, wherein the signaling comprises at least of: types of the pending transmissions; traffic types, service types, application types, priority indicators, logical channels or logical channel groups associated with the pending transmissions; time when the pending transmissions are expected to start; duration in which the pending transmissions are expected to last; and a data volume associated with the pending transmissions.

38. The method of any of examples 28-38, wherein the second terminal device enters the active state in one of the following modes: immediately upon reception of the signaling; at an expected time indicated by the signaling; and at an estimated time from reception of the signaling.

39. The method of example 38, wherein the estimated time is determined by the second terminal device based on a resource congestion level on resource pools.

40. The method of example 39, wherein the resource congestion level is determined based on a channel busy ratio, or a channel usage ratio, or a hybrid automatic repeat request negative acknowledgement ratio.

41. The method of any of examples 28-40, wherein configurations of the first terminal device and the second terminal device are signaled by a control node or preconfigured.

42. The method of any of examples 29-31 and 41, wherein the control node is a gNB, or a controlling terminal device, or a combination of the gNB and the controlling terminal device.

43. A first terminal device (800), comprising: a processor (801); and a memory (802) communicatively coupled to the processor and adapted to store instructions which, when executed by the processor, cause the first terminal device to perform operations of the method of any of examples 1-14.

44. A control node (1000), comprising: a processor (1001); and a memory (1002) communicatively coupled to the processor and adapted to store instructions which, when executed by the processor, cause the control node to perform operations of the method of any of examples 15-27.

45. A second terminal device (1200), comprising: a processor (1201); and a memory (1202) communicatively coupled to the processor and adapted to store instructions which, when executed by the processor, cause the second terminal device to perform operations of the method of any of examples 28-42.

46. A wireless communication system (1400), comprising: a first terminal device (1401) of example 43; a control node (1402) of example 44, communicating with at least the first terminal device; and a second terminal device (1403) of example 45, communicating with at least the first terminal device and the control node.

47. A non-transitory computer readable medium having a computer program stored thereon which, when executed by a set of one or more processors of a first terminal device, causes the first terminal device to perform operations of the method of any of examples 1-14. 48. A non-transitory computer readable medium having a computer program stored thereon which, when executed by a set of one or more processors of a control node, causes the control node to perform operations of the method of any of examples 15-27.

49. A non-transitory computer readable medium having a computer program stored thereon which, when executed by a set of one or more processors of a second terminal device, causes the second terminal device to perform operations of the method of any of examples 28-42.

Claims

1. A method (500) implemented by a first terminal device, the method comprising: transmitting (501), to a control node, a first signaling indicating that the first terminal device has pending transmissions on a sidelink towards a second terminal device; receiving (502) a sidelink grant from the control node; and initiating (503) transmissions on the sidelink to the second terminal device based on the sidelink grant.

2. The method of claim 1, wherein the first signaling is transmitted via at least one of: a scheduling request, SR, on a physical uplink control channel, PUCCH; a buffer status report on a physical uplink shared channel, PUSCH; a random access channel, RACH, transmission; a non-SR transmission on the PUCCH; and a sounding reference signal, SRS, transmission.

3. The method of claim 2, wherein:

- the scheduling request is triggered by at least one of: arrival of new sidelink transmissions on the sidelink, and trigger of sidelink channel state information, CSI, reporting; and/or

- the RACH transmission is one of the following: an Msgl transmission in the case of 4-step RACH procedure, an MsgA transmission in the case of 2-step RACH procedure, an Msg3 transmission in the case of 4-step RACH procedure, and an Msg5 transmission in the case of 4-step RACH procedure.

4. The method of claim 2 or 3, wherein: - in the case that the first signaling is transmitted via the RACH transmission, dedicated physical random access channel, PRACH, or RACH occasions are allocated to the first terminal device to indicate that the first terminal device has pending sidelink transmissions towards one or more terminal devices; and/or

- an indicator indicating that the first terminal device has the pending transmissions on the sidelink towards the second terminal device and included in the RACH transmission is carried in a media access control, MAC, subheader, or in a MAC control element, CE, or in a radio resource control, RRC, message during the RACH transmission; and/or

- in the case that the first signaling is transmitted via the SR or the non-SR transmission on the PUCCH and/or the SRS transmission, PUCCH resources and/or SRS resources are allocated to the first terminal device to indicate that the first terminal device has pending sidelink transmissions towards one or more terminal devices.

5. The method of any of claims 1-4, further comprising: transmitting, to the second terminal device, a second signaling indicating that the first terminal device has the pending sidelink transmissions towards the second terminal device.

6. The method of claim 5, wherein the second signaling is at least one of:

PC5-RRC signaling;

MAC CE; a control protocol data unit, PDU, of a protocol layer; and layer 1, LI, signaling, wherein, optionally:

- in the case that the second signaling is at least one of the PC5-RRC signaling, the MAC CE and the control PDU, configured sidelink grants are allocated to the first terminal device to transmit the second signaling; and/or

- the LI signaling includes at least one of: LI signaling on a physical sidelink control channel, PSCCH; and LI signaling on a physical sidelink shared channel, PSSCH.

7. The method of claim 5 or 6, wherein the second signaling comprises at least of: types of the pending transmissions; traffic types, service types, application types, priority indicators, logical channels or logical channel groups associated with the pending transmissions; time when the pending transmissions are expected to start; duration in which the pending transmissions are expected to last; and a data volume associated with the pending transmissions.

8. The method of any of claims 1-7, wherein:

- configurations of the first terminal device and the second terminal device are signaled by the control node or preconfigured; and/or

- the control node is a gNB, or a controlling terminal device, or a combination of the gNB and the controlling terminal device.

9. A method (600) implemented by a control node, the method comprising: receiving (601), from a first terminal device, a first signaling indicating that the first terminal device has pending transmissions on a sidelink towards a second terminal device; and transmitting (602) a sidelink grant to the first terminal device.

10. The method of claim 9, wherein the first signaling is received via at least one of: a scheduling request, SR, on a physical uplink control channel, PUCCH; a buffer status report on a physical uplink shared channel, PUSCH; a random access channel, RACH, transmission; a non-SR transmission on the PUCCH; and a sounding reference signal, SRS, transmission.

11. The method of claim 10, wherein the RACH transmission is one of the following: an Msgl transmission in the case of 4-step RACH procedure; an MsgA transmission in the case of 2-step RACH procedure; an Msg3 transmission in the case of 4-step RACH procedure; and an Msg5 transmission in the case of 4-step RACH procedure.

12. The method of claim 10 or 11, wherein:

- the method further comprises: in the case that the first signaling is received via the RACH transmission, allocating dedicated physical random access channel, PRACH, or RACH occasions to indicate that the first terminal device has pending sidelink transmissions towards one or more terminal devices; and/or

- an indicator indicating that the first terminal device has the pending transmissions on the sidelink towards the second terminal device and included in the RACH transmission is carried in a media access control, MAC subheader, or in a MAC control element, CE, or in a radio resource control, RRC, message during the RACH transmission; and/or

- the method further comprises: in the case that the first signaling is received via the SR or the non-SR transmission on the PUCCH and/or the SRS transmission, allocating PUCCH resources and/or SRS resources to indicate that the first terminal device has pending sidelink transmissions towards one or more terminal devices.

13. The method of any of claims 9-12, further comprising: transmitting, to the second terminal device, a signaling indicating that the first terminal device has the pending sidelink transmissions towards the second terminal device.

14. The method of claim 13, wherein:

- the signaling is transmitted to the second terminal device via at least one of:

RRC signaling, MAC CE, and layer 1, LI, signaling; and/or

- the signaling transmitted to the second terminal device is used by the control node to wake up the second terminal device.

15. The method of claim 13 or 14, wherein:

- the signaling transmitted to the second terminal device comprises at least of: types of the pending transmissions, traffic types, service types, application types, priority indicators, logical channels or logical channel groups associated with the pending transmissions, time when the pending transmissions are expected to start, duration in which the pending transmissions are expected to last, and a data volume associated with the pending transmissions; and/or

- the signaling is transmitted by way of a serving control node for the second terminal device.

16. The method of any of claims 9-15, wherein: - configurations of the first terminal device and the second terminal device are signaled by the control node or preconfigured; and/or

17. A method (700) implemented by a second terminal device, the method comprising: receiving (701) a signaling indicating that a first terminal device has pending transmissions on a sidelink towards the second terminal device; entering (702) an active state; and receiving (703) transmissions on the sidelink from the first terminal device.

18. The method of claim 17, wherein the signaling is received from a control node, wherein, optionally:

- the signaling is at least one of: radio resource control, RRC, signaling, media access control, MAC, control element, CE, and layer 1, LI, signaling; and/or

- the signaling is used by the control node to wake up the second terminal device.

19. The method of claim 17, wherein the signaling is received from the first terminal device, wherein, optionally, the signaling is at least one of:

PC5-RRC signaling,

MAC CE, a control protocol data unit, PDU, of a protocol layer, and LI signaling, wherein, optionally, the LI signaling includes at least one of:

LI signaling on a physical sidelink control channel, PSCCH, and LI signaling on a physical sidelink shared channel, PSSCH.

20. The method of claim 19, wherein:

- the second terminal device is configured with periodic occasions in time for reception of the signaling, regardless of whether a sidelink discontinuous reception state of the second terminal device is active; or

- the second terminal device is active only during occasions which are overlapped with a discontinuos reception active time.

21. The method of any of claims 17-20, wherein the signaling comprises at least of: types of the pending transmissions; traffic types, service types, application types, priority indicators, logical channels or logical channel groups associated with the pending transmissions; time when the pending transmissions are expected to start; duration in which the pending transmissions are expected to last; and a data volume associated with the pending transmissions.

22. The method of any of claims 17-21, wherein the second terminal device enters the active state in one of the following modes: immediately upon reception of the signaling; at an expected time indicated by the signaling; and at an estimated time from reception of the signaling, wherein, optionally, the estimated time is determined by the second terminal device based on a resource congestion level on resource pools, wherein, optionally, the resource congestion level is determined based on a channel busy ratio, or a channel usage ratio, or a hybrid automatic repeat request negative acknowledgement ratio.

23. The method of any of claims 17-22, wherein configurations of the first terminal device and the second terminal device are signaled by a control node or preconfigured.

24. The method of any of claims 18 and 21-23, wherein the control node is a gNB, or a controlling terminal device, or a combination of the gNB and the controlling terminal device.