TECHNICAL FIELD

The present disclosure relates generally to the field of mobile communications, to methods for transmission and reception of data in a time-slotted unlicensed sidelink (SL-U) radio channel, and to according computer programs and user equipment (UE) devices.

BACKGROUND ART

For Release 18 of its NR/5G- Advanced specification, the 3 ^rd Generation Partnership Project (3 GPP) has initiated a study on the use of unlicensed bands in the sidelink (SL) of mobile communication systems. The presence of other radio access technologies (RATs), like Wi-Fi, imposes new challenges for the channel access mechanisms and the physical layer (PHY) design of the sidelink with unlicensed bands.

Before transmitting in unlicensed spectrum, a UE device may have to sense the channel, i.e., perform listen-before-talk (LBT), to ensure that no other device is transmitting on the resources it intends to use. After clearing LBT in the unlicensed band, i.e., after sensing the channel to be free, the UE device can start its transmission.

Generally, a sensing slot granularity of the various LBT types is not aligned with the symbol or slot granularity of SL-unlicensed (SL-U) communication, e.g., the sensing slot granularity of Type 1 LBT is 9ps, while the smallest slot duration of NR is 0.125ms.

In SL-U communication, the access to the radio channel is on a slot basis. The slot-based access of SL-U UEs means that, after clearing LBT, the respective UE should start its transmission at the starting symbol of the next slot, i.e., at the beginning of the next slot. Therefore, a UE in SL-U would normally have to wait for the beginning of the next slot to transmit.

Due to the waiting time from the moment LBT was cleared till the start of its transmission, a SL-U Tx UE may have to perform another short sensing operation right before it starts its transmission to verify that the channel is still free. Besides the transmission delay, waiting for the next starting opportunity/symbol may block a SL-U Tx UE from accessing the channel, as a UE in another RAT may occupy the channel in the meantime. For example, a Wi-Fi UE may start transmitting its frame immediately after clearing LBT. Hence, with its short sensing shortly before the beginning of the next slot, the SL-U UE may detect that the channel has been occupied, and therefore miss the transmit occasion (starting opportunity/symbol).

In order to improve channel access for SL-U UEs, it has been proposed to have additional starting opportunities/ symbols within a slot, besides the single starting opportunity/symbol per slot supported in NR SL, and to enable multi-slot consecutive transmissions.

Currently a transmission within a slot in NR SL is indicated with the presence of a Physical Sidelink Control CHannel (PSCCH) at the single starting opportunity/symbol within a slot. The PSCCH carries a first-stage portion of sidelink control information (SCI). In NR SL, a data transmission is carried in a Physical Sidelink Shared CHannel (PSSCH). In NR SL, a second- stage portion of the SCI is multiplexed with PSSCH.

Having multiple starting symbols in an NR SL slot introduces an ambiguity in the actual start of a transmission within a slot. Prior art solutions require the transmission of PSCCH at the start of a transmission to allow other UEs to identify the actual starting symbol. This means that other UEs, which are unaware whether there is a transmission in a sub-channel and if so, which is the starting symbol of the transmission, have to search for PSCCH at all possible starting symbols in each sub-channel.

More specifically, SL-U UEs have to search for PSCCH at the multiple starting opportunities/symbols to decode a first-stage portion of the SCI to sense the channel (for transmission), and to decode a second-stage portion of the SCI to determine whether the respective Rx UE is the destination of a transmission (for reception). Hence, for N possible starting opportunities/symbols per slot, the prior art solutions result in N times the complexity for monitoring the PSCCH and the SCI.

SUMMARY

It is an objective to overcome these and other drawbacks. The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect, a method is provided for transmission of data in a time-slotted unlicensed sidelink, SL-U, radio channel. The method comprises transmitting, in a time slot, an indication whether the data is included in a prior time slot, starting from one of multiple starting opportunities per time slot.

This supports sensing based on mode-2 resource assignment (i.e., the UE selecting from a resource pool a resource for transmission as well as reception in SL-U communications) with multiple possible starting opportunities/symbols within a time slot. The main benefit is that the increase of UE implementation complexity for monitoring additional possible starting opportunities/symbols is avoided, while reducing a waiting time for the start of the transmission, and, consequently, improving the channel access success rate. The sensing or data receiving UEs need to monitor only one location within a time slot for each sub-channel, as in NR SL. This location is the same location in a time slot as currently in NR SL.

Time-slotting as used herein may refer to a communication scheme that implies an organization of resources in accordance with a time division multiplex (TDM) scheme (i.e., sequential time slots).

Sidelink communication as used herein may refer to a direct communication between terminal devices (UEs) without cellular network support (i.e., not going through a base station).

Unlicensed communication as used herein may refer to communication based on unlicensed spectrum.

Data as used herein may refer to “payload” data, such as a transport block (TB) in a 3 GPP system.

A resource pool as used herein may refer to a set of radio resources assigned to sidelink operation.

In a possible implementation form, further data may be transmitted in the time slot. This enables multi-slot consecutive transmission.

Further data as used herein may also refer to “payload” data, and may or may not form a continuation of the data mentioned previously.

In a possible implementation form, the method may further comprise sensing whether the SLIT radio channel is free; and transmitting the data in the prior time slot starting from the one of the multiple starting opportunities per time slot if the SL-U radio channel is free.

Sensing as used herein may refer to a listening in communications, i.e., being receptive.

This avoids collisions and thus improves a channel access success rate.

In a possible implementation form, the sensing whether the SL-U radio channel is free may further comprise sensing whether the SL-U radio channel is free in accordance with a listen- before-talk, LBT, procedure.

Listen-before-talk (LBT) as used herein may refer to a protocol enabling a coordinated use of a shared medium, such as a radio channel, by multiple users, wherein a UE performs sensing (“listening”) to check if the channel is free before transmitting (“talking”).

This re-uses LBT procedures originally established for New Radio unlicensed (NR-U) communications.

According to a second aspect, a method is provided for reception of data in a time-slotted unlicensed sidelink, SL-U, radio channel. The method comprises receiving, in a time slot, an indication whether the data is included in a prior time slot, starting from one of multiple starting opportunities per time slot.

This reception method corresponds to the transmission method of the first aspect in terms of effects and advantages. In a possible implementation form, the method may further comprise buffering the prior time slot.

This trades a small additional delay for the ability to decode data included in the prior time slot.

In a possible implementation form, the buffering of the prior time slot may comprise buffering the prior time slot starting from a preconfigured starting symbol.

This has the advantage that the buffering can be done more efficiently and that a latency due to delayed processing of data included in the prior time slot is minimized.

Buffering as used herein may refer to a form of short-term temporary storage.

(Pre-)configuration as used herein may refer to a configuration of/signaling to the UE by the network, or may refer to a predefined configuration in the UE being used when the UE is out of network coverage.

A symbol as used herein may refer to an element of a time slot. A starting symbol as used herein may refer to a symbol of the time slot where a transmission or reception of the data may start.

In a possible implementation form, the buffering of the prior time slot may be preconfigured per resource pool.

This enables a differentiation of the buffering of the prior time slot between resource pools having full slot structure and mini-slot structure, for example. It also enables differentiation of the buffering of the prior time slot between sensing UEs and Rx UEs.

In a possible implementation form, the method may further comprise decoding the data included in the prior time slot, starting from the one of the multiple starting opportunities per time slot, in response to the indication that the data is included in the prior time slot.

Decoding as used herein may refer to processing an electronic signal, e.g. a sampled waveform comprising complex values, into a binary form that can be interpreted by client layers. In a possible implementation form, the one of the multiple starting opportunities per time slot may comprise a next one of the multiple starting opportunities per time slot.

This reduces a waiting time for the start of the transmission, and, consequently, improves the channel access success rate.

In a possible implementation form, the indication whether the data is included in the prior time slot may start from any one of the multiple starting opportunities per time slot in the time slot.

This trades standards compliance for flexibility as regards the arrangement, within the time slot, of the indication whether the data is included in the prior time slot.

In a possible implementation form, the indication whether the data is included in the prior time slot may start from a first one of the multiple starting opportunities per time slot in the time slot.

This ensures standards compliance as regards the arrangement, within the time slot, of the indication whether the data is included in the prior time slot.

In a possible implementation form, the indication whether the data is included in the prior time slot may be indicative of a starting symbol of the data in the prior time slot.

This enables a direct encoding of the starting symbol of the data in the indication, or an indirect encoding of the starting symbol of the data in the indication, e.g. as an index into a lookup table.

In a possible implementation form, the multiple starting opportunities per time slot may be preconfigured.

This enables network control of the SL-U communication or to preconfigure per resource pool the multiple starting opportunities per time slot.

In a possible implementation form, the indication whether the data is included in the prior time slot may comprise a number of bits corresponding to a next larger integer of a logarithm dualis of a total number of the multiple starting opportunities per time slot. This minimizes a size of the indication whether the data is included in the prior time slot.

In a possible implementation form, the total number of the multiple starting opportunities per time slot may comprise two starting opportunities per time slot; and the indication whether the data is included in the prior time slot may comprise one bit.

This provides a practical implementation.

In a possible implementation form, the time slot may succeed the prior time slot.

This allows for transmissions in consecutive time slots.

In a possible implementation form, a physical sidelink control channel, PSCCH may comprise the indication whether the data is included in the prior time slot.

This generalizes the standards compliant solution according to which the PSCCH comprises an indication whether the data is included in the same time slot.

In a possible implementation form, a sidelink control information, SCI, of the time slot may comprise the indication whether the data is included in the prior time slot.

In a possible implementation form, a first-stage portion of the SCI may comprise the indication whether the data is included in the prior time slot.

In a possible implementation form, reserved bits of the first-stage portion of the SCI may comprise the indication whether the data is included in the prior time slot.

In a possible implementation form, resource reservation bits of the first-stage portion of the SCI may comprise the indication whether the data is included in the prior time slot.

In a possible implementation form, a second-stage portion of the SCI may comprise the indication whether the data is included in the prior time slot.

This provides numerous implementation alternatives. In a possible implementation form, the SCI may comprise another indication of another SCI in the prior time slot.

According to a third aspect, a computer program is provided, comprising a program code for performing a method according to the first aspect or a method according to the second aspect, when executed on a computer.

The computer program corresponds to the transmission method of the first aspect and to the reception method of the second aspect in terms of effects and advantages.

According to a fourth aspect, a user equipment, UE, device is provided for transmission of data in a time-slotted unlicensed sidelink, SL-U, radio channel. The UE comprises a processor, being configured to transmit, in a time slot, an indication whether the data is included in a prior time slot, starting from one of multiple starting opportunities per time slot.

The Tx UE device corresponds to the transmission method of the first aspect in terms of effects and advantages.

According to a fifth aspect, a user equipment, UE, device is provided for reception of data in a time-slotted unlicensed sidelink, SL-U, radio channel. The UE comprises a processor, being configured to receive, in a time slot, an indication whether the data is included in a prior time slot, starting from one of multiple starting opportunities per time slot.

The Rx UE device corresponds to the reception method of the second aspect in terms of effects and advantages.

BRIEF DESCRIPTION OF DRAWINGS

The above-described aspects and implementations will now be explained with reference to the accompanying drawings, in which the same or similar reference numerals designate the same or similar elements. The drawings are to be regarded as being schematic representations, and elements illustrated in the drawings are not necessarily shown to scale. Rather, the various elements are represented such that their function and general purpose become apparent to those skilled in the art.

FIG. 1 illustrates communication roles according to the present disclosure;

FIG. 2 illustrates SL-U communication according to 3GPP standards;

FIG. 3 illustrates SL-U communication according to the present disclosure;

FIG. 4 illustrates methods according to the present disclosure for transmission/reception of data in a time-slotted SL-U radio channel;

FIG. 5 illustrates SL-U communication according to the present disclosure given that the data is not included in the prior time slot;

FIGs. 6-10 illustrate various options according to the present disclosure for providing the indication whether the data is included in the prior time slot; and

FIG. 11 illustrates an implementation option according to the present disclosure for providing another indication of another SCI in the prior time slot.

DETAILED DESCRIPTIONS OF DRAWINGS

In the following description, reference is made to the accompanying drawings, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the present disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding apparatus or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise.

FIG. 1 illustrates communication roles according to the present disclosure.

When data is transmitted in a time-slotted SL-U radio channel 6 by a UE device 1 starting from the next possible starting opportunity/ symbol of the multiple starting opportunities per slot, this actual starting opportunity/symbol and the occupied sub-channel(s) are unknown to other UE devices 1’, 3, 3’.

These other UE devices include (sensing) Tx UEs 1 ’ which intend to transmit transport blocks (TB) and Rx UEs 3, 3’ aiming to receive data, including target Rx UEs 3 that are the destination of a TB sent by a Tx UE 1 and non-target Rx UEs that are not the destination of a TB sent by a Tx UE 1.

FIG. 2 illustrates SL-U communication according to 3GPP standards.

An SL-U radio channel 6 is indicated on the right of FIG. 2 as a cylindric shape. Generally, the unlicensed (U) radio channel 6 is unslotted. However, SL communication implies an organization of resources in accordance with a TDM scheme (i.e., sequential time slots) on the radio channel 6, so that SL-U communication takes place in a time-slotted SL-U radio channel 6.

Fig. 2 further indicates two exemplary time slots 61, 62. According to the indicated exemplary slot structure, a slot comprises 14 orthogonal frequency division multiplexing (OFDM) symbols, wherein the beginning of the respective slot 61, 62 coincides with a single starting opportunity/symbol 611, 621.

Typically, the first symbol of a time slot 61, 62 is dedicated to AGC 611, 621, so that a Rx UE 3, 3’ can adjust the received signal power according to the dynamic range of its analog-to- digital converters (ADCs). The next 2 or 3 symbols carry a PSCCH 623, which includes a 1 ^st stage SCI. In the 1 ^st stage SCI, a Tx UE 1 indicates the occupied sub-channels of its current transmission and may announce up to two reservations of resources for subsequent (re)transmissions. The information carried in the 1 ^st stage SCI is monitored and used by other (sensing) Tx UEs 1’ using the same resource pool, so as to identify potentially available resources for their transmissions, i.e. for mode-2 sensing in NR SL.

A resource pool as used herein may refer to available SL resources which may be (pre-)configured to be used by several UEs for their SL transmissions and/or reception.

A 2 ^nd stage SCI, which contains an indication of the source ID and destination ID of the transmission, is multiplexed with a physical sidelink shared channel (PSSCH) 624, and is used by Rx UEs 3, 3’ to receive a transmission. The PSSCH may also carry a TB sent by a Tx UE 1. Some of the symbols of a time slot 61, 62 carry the demodulation reference signal (DMRS), which is used for channel estimation.

Before transmitting in unlicensed spectrum, the Tx UE device 1 may have to sense the channel, i.e., perform listen-before-talk (LBT), to ensure that no other device is transmitting on the resources it intends to use. After clearing LBT in the unlicensed band, i.e., after sensing the channel to be free, the Tx UE device 1 can start its transmission.

Generally, a sensing slot granularity of the various LBT types is not aligned with the symbol or slot granularity of SL-U communication, e.g., the sensing slot granularity of Type 1 LBT is 9ps, while the smallest slot duration of NR is 0.125ms.

In SL-U communication, the access to the radio channel 6 is on a slot basis. The slot-based access of SL-U UEs means that, after clearing LBT, for example at time instant t = to, the respective Tx UE 1 should start its transmission at the starting opportunity/symbol of the next slot, i.e., at the beginning of the time slot 62 at time instant t = . Therefore, a Tx UE 1 in SL- U would normally have to wait for the beginning of the next slot 62 to transmit.

Due to the waiting time At = ts-to from the moment LBT was cleared at t = to till the potential start of its transmission at t = ts, a SL-U Tx UE 1 may have to perform another short sensing operation right before it starts its transmission to verify that the channel 6 is still free. Besides the transmission delay, waiting for the next starting opportunity/symbol may block a SL-U TX UE 1 from accessing the channel 6, as a UE in another RAT may occupy the channel in the meantime, for example at time instant t = t2. For example, a Wi-Fi UE may start transmitting its frame 63 immediately after clearing LBT. Hence, with its short sensing shortly before the beginning of the next slot 62, the SL-U Tx UE may detect that the channel 6 has been occupied, and therefore miss the transmit occasion (starting opportunity/symbol).

When not missing the transmit occasion, the data may be transmitted in the PSSCH symbols 624 of said next time slot 62.

FIG. 3 illustrates SL-U communication according to the present disclosure.

The SL-U communication according to the present disclosure assumes multiple possible (pre-) configured starting symbols within a time slot, such that a Tx UE 1 in SL-U starts its transmission at a next possible starting symbol.

In order to avoid that Rx UEs 3, 3’ have to monitor all possible starting symbols in every subchannel, a Tx UE 1 may send an indication 625 in a next time slot 62 that indicates whether the data 614 is included in a prior time slot 61 (reverse indication).

Multiple starting opportunities/ symbols 611, 612, 621, 622 within a time slot 61, 62 may, for example, be supported by dividing the known slot structure into multiple mini-slots. FIG. 3 shows an example with N=2 starting opportunities/ symbols per time slot 61, 62, one at the start (symbol 0) and one at the middle (symbol 7) of the respective slot.

When allocated, the respective mini-slot may include an AGC symbol at the respective starting opportunity/symbol 611, 612, 621, 622 - in other words, the possible starting symbols may or may not be AGC symbols.

Furthermore, the respective mini-slot may include a PSCCH 623. The actual starting opportunity/symbol of a transmission may be identified based on the PSCCH 623, i.e., in the same way that the start of a transmission with only one starting opportunity/symbol per slot is identified currently in NR SL. Due to the shortened waiting time At = ti-to from the moment LBT was cleared at t = to till the potential start of its transmission at t = ty, waiting for the next starting opportunity/symbol 612 may block a SL-U Tx UE 1 from accessing the channel 6 with considerably less probability. A UE in another RAT may still occupy the channel in the meantime. However, in the example of FIG. 3, transmission of the Wi-Fi frame 63 cannot start from time instant t = h anymore, as the SL-U Tx UE 1 has accessed the channel first at t = ti. Hence, the SL-U Tx UE 1 may make use of the transmit occasion.

As such, time slot 61 may include the data 614 to be transmitted starting from one 612 of the multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62 if the SL-U radio channel 6 is free, and time slot 62 may include an indication 625 whether the data 614 is included in the time slot 61, starting from the one 612 of the multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62.

Once an SL-U Tx UE 1 has accessed a channel 6 in a slot 61, e.g. in the middle of a slot, it may continue transmitting in the next slot 62 as well (multi-slot consecutive transmission) if it is interested in holding onto the channel 6 as much as possible, e.g., to satisfy traffic requirements. As such, further data 624 may be transmitted in the time slot 62.

The underlying methods 2, 4 of the SL-U communication according to the present disclosure will be explained next.

FIG. 4 illustrates methods 2, 4 according to the present disclosure for transmission/reception of data 614 in a time-slotted SL-U radio channel 6.

A flow chart of the method 2 (hereinafter: transmission method) of the first aspect for the transmission of the data 614 is shown on the left of FIG. 4. The method 2 may be performed by a corresponding Tx UE device 1 of the fourth aspect shown on the top-left of FIG. 4. The Tx UE device 1 comprises a processor 11 which is configured to perform the steps of the method 2 in accordance with a computer program comprising a program code for performing the method 2.

A flow chart of the method 4 (hereinafter: reception method) of the second aspect for the reception of the data 614 is depicted on the right of FIG. 4. The method 4 may be performed by a corresponding Rx UE device 3 of the fifth aspect shown on the top-right of FIG. 4. The Rx UE device 3 comprises a processor 31 which is configured to perform the steps of the method 4 in accordance with a computer program comprising a program code for performing the method 4.

As previously suggested in FIG. 1, both methods 2, 4 communicate via the time-slotted SL-U radio channel 6 indicated as a cylindric shape in the center of FIG. 4.

On the transmit side, the transmission method 2 may comprise a step of sensing 21 whether the SL-U radio channel 6 is free. For example, the sensing 21 whether the SL-U radio channel 6 is free may comprise sensing 211 whether the SL-U radio channel 6 is free in accordance with an LBT procedure. For NR-unlicensed (NR-U) different types of LBT have been defined to support channel access (i.e. Type 1 LBT, Type 2 LBT) and the adoption of similar methods for SL-U has also been proposed.

The transmission method 2 may comprise a step of transmitting 22 the data 614 in a prior time slot 61 starting from one 612 of the multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62 if the SL-U radio channel 6 is free, as determined by the sensing 21 step.

The transmission method 2 comprises a step of transmitting 23, in a time slot 62, an indication 625 whether the data 614 is included in the prior time slot 61, starting from the one 612 of the multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62.

On the receive side, the reception method 4 may comprise a step of buffering 42 the prior time slot 61. For example, the buffering 42 of the prior time slot 61 may comprise buffering 421 the prior time slot 61 starting from a preconfigured starting symbol. In other words, the locations of the possible starting symbols 611, 612, 621, 622 in a time slot 61, 62 determine which part of the prior slot 61 may require buffering. For the example of FIG. 3 with an additional starting symbol 612, 622 at the middle of the respective slot 61, 62, the second half of the prior time slot 61 may be buffered. The buffering 42, 421 of the prior time slot 61 may be preconfigured based on the type of UE, i.e. sensing UEs or Rx UEs, or per resource pool. For example, UEs in a Tx resource pool may be (pre-)configured to not buffer part of the previous slot (based on possible starting symbols), and UEs in a Rx resource pool may be (pre-)configured to buffer part of the previous slot (based on possible starting symbols). For an example with two additional starting symbols at symbols 5 and 9 of the respective slot 61, 62, the prior time slot 61 may be buffered starting from symbol 5. The buffering 42, 421 of the prior time slot 61 may be preconfigured per resource pool.

Generally, the (pre-)configuration of the starting opportunity/ symbol can be done based on the type of transmission, service or application. If a Rx UE 3, 3’ is interested in receiving just one type of service, then it only needs to buffer based on the (pre-)configured starting symbols for that service. A Tx UE 1, 1’ could also be (pre-)configured to consider only certain starting symbols for a transmission depending on the service.

The reception method 4 comprises a step of receiving 43, in the time slot 62, an indication 625 whether the data 614 is included in the prior time slot 61, starting from the one 612 of multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62.

This means that if an Rx UE 3, 3’, after decoding the PSCCH 623 and the 2 ^nd stage SCI multiplexed with the PSSCH 624 at time slot 62, determines that it is a target Rx UE 3 of the TB carried by the PSSCH 624 at slot 62, it then further determines (i) if there was also data 614 sent in slot 61 starting from one of the additional starting symbols and (ii) if so, the starting opportunity/ symbol 612 of the data 614 at slot 61.

Note that the reverse indication may not only indicate the additional starting symbol 612 at which a transmission started in the prior slot 61. It may also indicate that no transmission started at any of the additional starting symbols 612 of the prior slot 61. Further note that the reverse indication may only need to be present in a current slot 62 if there was a transmission that started in one of the additional starting symbols 612 in the prior slot 61.

Based on the starting symbol indicated by the reverse indication, a target Rx UE 3 is aware of which part of the buffered data of the prior slot 61 it has to use for decoding the data 614.

The reception method 4 may further comprise a step of decoding 44 the data 614 included in the prior time slot 61, starting from the one 612 of the multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62, in response to the indication 625 that the data 614 is included in the prior time slot 61. It applies to both methods 2, 4 that the time slot 62 may succeed the prior time slot 61.

It also applies to both methods 2, 4 that the one 612 of the multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62 may comprise a next one of the multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62. For example, with respect to time instant t = to in FIG. 3, the next one of the multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62 is represented by reference sign 612.

It further applies to both methods 2, 4 that the multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62 may be preconfigured. This may apply to a total number of the multiple starting opportunities/symbols per time slot and/or to the relative positions of the multiple starting opportunities/symbols 611, 612, 621, 622 within the time slots 61, 62. For example, FIG. 3 shows an example with N=2 starting opportunities/symbols per time slot 61, 62, one at the start (symbol 0) and one at the middle (symbol 7) of the respective slot. A further example with N=3 starting opportunities/symbols per time slot 61, 62 may include one at the start (symbol 0), another at symbol 5, and yet another at symbol 9 of the respective slot, for example.

It still applies to both methods 2, 4 that the indication 625 whether the data 614 is included in the prior time slot 61 may start from any one 621, 622 of the multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62 in the time slot 62. For example, the indication 625 whether the data 614 is included in the prior time slot 61 may start from a first one 621 of the multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62 in the time slot 62.

It furthermore applies to both methods 2, 4 that the indication 625 whether the data 614 is included in the prior time slot 61 may be indicative of a starting symbol of the data 614 in the prior time slot 61.

It additionally applies to both methods 2, 4 that the indication 625 whether the data 614 is included in the prior time slot 61 may comprise a number of bits corresponding to a next larger integer of a logarithm dualis of a total number N of the multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62: log ₂ N. For example, the total number of the multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62 may comprise N = 2 starting opportunities per time slot 61, 62; and the indication 625 whether the data 614 is included in the prior time slot 61 may comprise log ₂ 2 = 1 bit. Generally, the total number of the multiple starting opportunities 611, 612, 621, 622 per time slot 61, 62 may comprise N starting opportunities per time slot 61, 62; and the indication 625 whether the data 614 is included in the prior time slot 61 may comprise log ₂ N bit.

FIG. 5 illustrates SL-U communication according to the present disclosure given that the data 614 is not included in the prior time slot 61.

FIGs. 6-10 illustrate various implementations according to the present disclosure for providing the indication 625 whether the data 614 is included in the prior time slot 61.

In accordance with FIG. 6, a PSCCH 623 included in the time slot 62 may comprise the indication 625 whether the data 614 is included in the prior time slot 61.

In accordance with FIG. 7, an SCI 6231, 6241 of the time slot 62 may comprise the indication 625 whether the data 614 is included in the prior time slot 61.

In accordance with FIGs. 8-9, a first-stage portion 6231 of the SCI 6231, 6241 may comprise the indication 625 whether the data 614 is included in the prior time slot 61 in reserved bits (e.g., in one reserved bit) of the first-stage portion 6231 of the SCI 6231, 6241 (see FIG. 8) or in resource reservation bits of the first-stage portion 6231 of the SCI 6231, 6241 (see FIG. 9). In any of the two cases, an additional indication (not shown) may be provided in the first-stage portion 6231 of the SCI 6231, 6241 that the prior time slot 61 includes an additional PSCCH (not shown). Note that in the case of FIG. 9, the indication 625 in the first-stage portion 6231 of the SCI 6231, 6241 requires e.g. one bit to indicate that the resource reservation bits should be interpreted differently, because conventionally said resource reservation bits do not indicate whether the data 614 is included in the prior time slot 61.

In accordance with FIG. 10, a second-stage portion 6241 of the SCI 6231, 6241 multiplexed with the PSSCH 624 may comprise the indication 625 whether the data 614 is included in the prior time slot 61. For this purpose, a new format of the second-stage SCI portion 6241 can be considered.

FIG. 11 illustrates an implementation according to the present disclosure for providing another indication 626 of another SCI (not shown) in the prior time slot 61. In particular, the SCI 6231, 6241 illustrated in any one of FIGs. 7 - 10 may comprise this indication 626 of the other SCI in the prior time slot 61.

To summarize the present disclosure, sensing UEs 1’, i.e., UEs that intend to transmit, reduce their SCI monitoring complexity N times by using the proposed idea without any additional cost compared to the prior art. Rx UEs (target 3 and non-target 3’) achieve the SCI monitoring reduction at the expense of additional buffering of a part of the previous slot. It is worth noting here that Rx UEs already buffer at least one slot in NR SL, i.e., the current slot and in NR part of another slot may also be buffered (e.g., for coverage enhancement). For target Rx UEs 3, there is also a small delay in decoding the previous slot, which is less than the duration of a slot (e.g., equal to the duration of half a slot). Note that due to the non-guaranteed channel access in the unlicensed spectrum, this additional small delay may not have a large impact. Furthermore, due to the same reason, operation in the unlicensed spectrum may anyway not be suitable for latency-critical use cases and the use of unlicensed spectrum is envisioned for use cases with large bandwidth requirements.

The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.